independent

roland@catalogix.se

Microsoft

mbj@microsoft.com http://self-issued.info/

Uninett AS

andreas.solberg@uninett.no https://www.linkedin.com/in/andreassolberg/

Schibsted Media Group

samuel.gulliksson@gmail.com

Yubico

ve7jtb@ve7jtb.com http://www.thread-safe.com/

OpenID Connect Working Group OpenID Connect Federation The OpenID Connect standard specifies how a Relying Party (RP) can discover metadata about an OpenID Provider (OP), and then register to obtain RP credentials. The discovery and registration process does not involve any mechanisms of dynamically establishing trust in the exchanged information, but instead rely on out-of-band trust establishment. In an identity federation context, this is not sufficient. The participants of the federation MUST be able to trust information provided about other participants in the federation. OpenID Connect Federations specifies how trust can be dynamically obtained by resolving trust from a common trusted third party. While this specification is primarily targeting OpenID Connect, it is designed to allow for reuse by other protocols and in other use cases.

This specification describes how two entities that would like to interact can dynamically fetch and resolve trust and metadata for a given protocol through the use of third-party trust anchor. A trust anchor is an entity whose main purpose is to issue statements about entities, such as OpenID Connect Relying Parties, OpenID Providers, and participating organizations. An identity federation can be realized using this specification using one or more levels of trust issuers. This specification does not mandate a specific way or restrict how a federation may be built. Instead, the specification provides the basic technical trust infrastructure building blocks needed to build a dynamic and distributed trust network such as a federation. Note that this specification only concerns itself with how two entities in a federation get to know about each other it does not change any other functionality in OpenID Connect. Note that a company, as with any real-world organization, MAY be represented by more than one entity in a federation. OpenID Connect Federation trust chains rely on cryptographically signed JSON Web Token (JWT) documents, and the trust chain does not at all rely on TLS to establish trust.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

This specification uses the terms "Claim Name", "Claim Value", "JSON Web Token (JWT)", defined by JSON Web Token (JWT) and the terms "OpenID Provider (OP)" and "Relying Party (RP)" defined by OpenID Connect Core 1.0. This specification also defines the following terms: Something that has a separate and distinct existence and that can be identified in a context. All entities in an OpenID Connect federation MUST have a globally unique identifier. An URI that is globally unique and that is bound to one Entity. An entity statement is issued by an entity, which pertains to a subject entity and leaf entities. An entity statement is always a signed JWT. An entity that issues an entity statement that appears somewhere in between those issued by the trust anchor and the leaf entity in a trust chain. An entity defined by a certain protocol, e.g., OpenID Connect Relying Party or Provider. An entity that represents a trusted third party. A sequence of entity statements that represents a chain starting at a leaf entity and ending in a trust anchor.

An entity statement is issued by an entity and concerns a subject entity and leaf entities in a federation. An entity statement is always a signed JWT. All entities in a federation SHOULD be prepared to publish an entity statement about themselves. If they are not able to do so themselves someone else MUST do it for them. An entity statement is composed of the following claims: REQUIRED. The entity identifier of the issuer of the statement. If the iss and the sub are identical, the issuer is making a statement about itself. REQUIRED. The entity identifier of the subject REQUIRED. The time the statement was issued. Its value is a JSON number representing the number of seconds from 1970-01-01T0:0:0Z as measured in UTC until the date/time. See RFC 3339 for details regarding date/times in general and UTC in particular. REQUIRED. Expiration time on or after which the statement MUST NOT be accepted for processing. Its value is a JSON number representing the number of seconds from 1970-01-01T0:0:0Z as measured in UTC until the date/time. OPTIONAL. A JSON Web Key Set (JWKS) representing the public part of the subject entity's signing keys. The corresponding private key is used by leaf entities to sign entity statements about themselves, and intermediate entities to sign statements about other entities. The keys that can be found here are primarily intended to sign entity statements and SHOULD NOT be used in other protocols. This claim is only OPTIONAL for the entity statement returned from an OP when the client is doing explicit registration. In all other cases it is REQUIRED. Every JWK in the JWK Set MUST have a Key ID (kid). OPTIONAL. The entity statement MAY be specifically created for an entity. The entity identifier for that entity MUST appear in this claim. OPTIONAL. Array of strings representing the entity identifiers of intermediate entities or trust anchors that MAY issue an entity statement about the issuer entity. For all entities except for trust anchors that do not have any superiors this is REQUIRED and MUST NOT be the empty list []. This claim MUST be absent from an entity statement issued by a trust anchor with no superiors. OPTIONAL. JSON object including protocol specific metadata claims that represent the entity's metadata. Each key of the JSON object represents a metadata type identifier, and each value MUST be a JSON object representing the metadata according to the metadata schema of that metadata type. An entity statement MAY contain multiple metadata statements, but only one for each metadata type. If the iss of an entity statement points to the same entity as the sub, then the entity statement MUST contain a metadata claim. If iss and sub are not the same, then the entity statement MUST NOT contain a metadata claim. OPTIONAL. JSON object that describes a metadata policy. Each key of the JSON object represents a metadata type identifier, and each value MUST be a JSON object representing the metadata policy according to the metadata schema of that metadata type. An entity statement MAY contain multiple metadata policy statements, but only one for each metadata type. Only non-leaf entities MAY contain a metadata_policy claim. Leaf entities MUST NOT contain a metadata_policy claim. OPTIONAL. JSON object that describes a set of trust chain constraints. More about this in OPTIONAL. The crit (critical) entity statement claim indicates that extensions to entity statement claims defined by this specification are being used that MUST be understood and processed. It is used in the same way that crit is used for extension JWS header parameters that MUST be understood and processed. Its value is an array listing the entity statement claims present in the entity statement that use those extensions. If any of the listed extension entity statement claims are not understood and supported by the recipient, then the entity statement is invalid. Producers MUST NOT include entity statement claim names defined by this specification or names that do not occur as entity statement claim names in the entity statement in the crit list. Producers MUST NOT use the empty list [] as the crit value. OPTIONAL. The policy_language_crit (critical) entity statement claim indicates that extensions to the policy language defined by this specification are being used that MUST be understood and processed. It is used in the same way that crit is used for extension JSON Web Signature (JWS) header parameters that MUST be understood and processed. Its value is an array listing the policy language extensions present in the policy language statements that use those extensions. If any of the listed extension policy language extensions are not understood and supported by the recipient, then the entity statement is invalid. Producers MUST NOT include policy language names defined by this specification or names that do not occur in policy language statements in the entity statement in the policy_language_crit list. Producers MUST NOT use the empty list [] as the policy_language_crit value. OPTIONAL. JSON object that describes a set of trust marks. More about this in OPTIONAL. An OP MUST use this claim to tell the RP which trust anchor it chose to use when responding to an explicit client registration. The value of trust_anchor_id is the entity identifier of a trust anchor. The entity statement is signed using the private key of the issuer entity, in the form of a JSON Web Signature (JWS). Entities MUST support signing Entity Statements with the RSA SHA-256 algorithm (an alg value of RS256). Consequently entities MUST support signature verification where the statement was signed using RS256.

The following is a non-normative example of an entity statement before serialization and adding a signature. The example contains a critical extension jti (JWT ID) to the entity statement and one critical extension to the policy language regexp (Regular expression).

In an OpenID Connect Identity Federation, entities that together build a trust chain can be categorized as: An entity that represents a trusted third party. In an OpenID Connect Identity Federation, an RP or an OP. Neither a leaf nor a trust anchor. A trust chain begins with a leaf entity's self-signed entity statement, has zero or more entity statements issued by intermediates about subordinates, and ends with an entity statement issued by the trust anchor about the top-most intermediate (if there are intermediates) or the leaf entity (if there are no intermediates). A simple example: If we have an RP that belongs to organization A that is a member of federation F, the trust chain for such a setup will contain the following entity statements: a self-signed entity statement about the RP published by the RP, an entity statement about the RP published by Organization A, and an entity statement about Organization A published by Federation. F A trust chain MUST always be possible to order such that: If we name the entity statements ES[0] (the leaf entity's self-signed entity statement) to ES[i] (an entity statement issued by the trust anchor), i>0 then: The iss entity in one entity statement is always the sub entity in the next. ES[j]['iss'] == ES[j+1]['sub'], j=0,...,i-1 . There MUST always be a signing key carried in the jwks claim in ES[j] that can be used to verify the signature of ES[j-1], j=i,...,1 . It MUST be possible to verify the signature of ES[0] with one of the keys in ES[0]['jwks']. The signing key that MUST be used to verify ES[i] is distributed from the trust anchors to any entity that needs to verify a trust chain in some secure out-of-band way not described in this document.

This specification does allow new metadata types to be defined, to support use cases outside OpenID Connect federations. The metadata type identifier will uniquely identify which metadata specification to utilize. The metadata document MUST be a JSON document. Beyond that there is no restriction. Metadata used in federations typically reuses existing metadata standards. If needed, the metadata schema is extended with additional properties relevant in a federated context. For instance, for OpenID Connect Federations, this specification uses metadata values from OpenID Connect Discovery 1.0 and OpenID Connect Dynamic Client Registration 1.0 and adds additional values used for federations.

The metadata type identifier is openid_relying_party. All parameters defined in Section 2 of OpenID Connect Dynamic Client Registration 1.0 are allowed in a metadata statement. To that list is added: REQUIRED. Array of strings specifying the client registration types the RP wants to use. Values defined by this specification are automatic and explicit. OPTIONAL. A human-readable name representing the organization owning the RP. OPTIONAL. A URI pointing to a signed JWT having the entity's JWK Set as payload. The JWT is signed with a key that was included in the JWK that the entity published in its self-signed entity statement. A signed JWT can contain the following claims, all except keys defined in : REQUIRED. List of JWKs. REQUIRED. The "iss" (issuer) claim identifies the principal that issued the JWT. REQUIRED. This claim identifies the owner of the keys. It SHOULD be the same as the issuer. OPTIONAL. This claim identifies the time at which the JWT was issued. OPTIONAL. This claim identifies the time at which the JWT is no longer valid. There are more claims defined in ; of these, aud SHOULD NOT be used, since the issuer can not know who the audience is. nbf and jti are deemed to not be very useful in this context and are therefore to be omitted.

The following is a non-normative example of a signed JWKS before serialization and adding a signature.

The metadata type identifier is openid_provider. All parameters defined in Section 3 of OpenID Connect Discovery 1.0 are applicable. In addition, the following parameters are defined by this specification: REQUIRED. Array specifying the federation types supported. Federation type values defined by this specification are automatic and explicit. OPTIONAL. A human-readable name representing the organization owning the OP. It is intended to be used in the user interface, being recognized by the end users that would be using the OP to authenticate. OPTIONAL. URL of the OP's Federation specific Dynamic Client Registration Endpoint. If the OP supports explicit client registration as described in , then this claim is REQUIRED. OPTIONAL. In OpenID Connect Core, no client authentication is performed at the authentication endpoint. Instead, you can say that a request authentication is performed. What it amounts to is that the OP maps the information in the request to the information it has on the client, through static or dynamic registration. If the map is successful, then the request is permitted to proceed. Something similar happens when automatic registration is used. Since there has been no explicit registration, the OP will gather information about the RP using the process outlined in . Once it has the RP metadata, the OP can verify the information the RP provides in the request. We make this a bit more secure by demanding the use of the request parameter or pushed authorization. The claim value is a JSON object with members representing processes/endpoints and as values lists of request authentication methods that are supported by the authorization endpoint. In this specification we use the processes/endpoints: Authorization Request (AR) as described in Section 3 of OpenID Connect Core 1.0 and Pushed Authorization Request (PAR), as described in . The request authentication methods are: This uses a Request Object as described in OpenID Connect Core 1.0. More about this in . The authentication process is described in Section 9 of OpenID Connect Core 1.0. Note that if private_key_jwt is used, the audience of the signed JWT MUST be either the URL of the Authorization Server's Authorization Endpoint or the Authorization Server's entity identifier. Section 2.1 of . Section 2.2 of . The only request authentication method that can be used if doing authentication as described in OpenID Connect Core 1.0 is request_object. If pushed authorization is used then one of private_key_jwt, tls_client_auth and self_signed_tls_client_auth can be used. OPTIONAL. A URI pointing to a signed JWT having the entity's JWK Set as payload. The JWT is signed with a key that was included in the JWK that the entity published in its self-signed entity statement. The following is a non-normative example of OP metadata:'

The metadata type identifier is oauth_authorization_server. All parameters defined in Section 2 of RFC 8414 are applicable.

The metadata type identifier is oauth_client. All parameters defined in Section 2 of RFC 7591 are applicable.

The metadata type identifier is oauth_resource. There is no standard that specifies what parameters can occur in the metadata for this kind of entity. So for the time being, this can be regarded as a placeholder.

The metadata type identifier is federation_entity. All entities participating in a federation are of this type. The following properties are allowed: OPTIONAL. The endpoint for the Federation API described in . Intermediate entities and trust anchors MUST publish a federation_api_endpoint. Leaf entities MUST NOT. OPTIONAL. String. The human-readable name describing the subject entity. This MAY be, for example, the name of an organization. OPTIONAL. JSON array with one or more strings representing contact persons at the entity. These MAY contain names, e-mail addresses, descriptions, phone numbers, etc. OPTIONAL. URL to documentation of conditions and policies relevant to this entity. OPTIONAL. URL to a generic home page representing this entity. OPTIONAL. A JSON array of signed JSON Web Token each representing a certification mark. More about certification marks in Example

An entity can publish metadata policies pertaining to entities of a specific type. Entity type identifiers specified in this document can be found in . Each such metadata policy has the following structure: It consists of one or more policy entries. Each policy entry applies to one metadata parameter, such as id_token_signing_alg. Each policy entry consists of one or more operators, which can be value modifiers or value checks. An operator can only appear once in a policy entry. It SHOULD be noted that claim names without language tags are different from the same claim but with language tags.

An example of a policy entry:

Which fits into a metadata policy like this:

Value modifiers are: Disregarding what value the parameter had, if any, the parameter's value will be set to the operator's value. Adds the value or values specified to the metadata parameter. If any of the specified values are already present as values of the parameter, they will not be added. If the parameter has no value, then the parameter is initialized with the specified value(s). If no value is assigned to this parameter, then the parameter's value will be set to the operator's value(s). Value checks are: The value of the parameter MUST be one of the ones listed in this directive. The resulting value of the parameter will be the intersection of the values in the directive and the values of the parameter. The values of the parameter MUST contain the ones in the directive. We define superset the mathematical way, that is, equality is included. If true, then the parameter MUST have a value.

As stated, a policy entry can contain one or more operators. Not all operators are allowed to appear together in a policy entry. subset_of and superset_of applies to parameters that can have more than one value (for instance, contacts) while one_of applies to parameters that can only have one value (for instance, id_token_signed_response_alg). This means that one_of cannot appear beside subset_of/ superset_of in a policy entry. value overrides everything else. So having value together with any other operator (except for essential) does not make sense. Other restrictions are: If subset_of and superset_of both appears as operators then the list of values in subset_of MUST be a superset of the values in superset_of. If add appears in a policy entry together with subset_of then the value/values of add MUST be a subset of subset_of. If add appears in a policy entry together with superset_of then the values of add MUST be a superset of superset_of. If default appears in a policy entry together with subset_of then the values of default MUST be a subset of subset_of. If default appears in a policy entry together with superset_of then the values of default MUST be a superset of superset_of. If add appears in a policy entry together with one_of then the value of add MUST be a member of one_of. If default appears in a policy entry together with one_of then the value default MUST be a member of one_of.

If there is more than one metadata policy in a trust chain, then the policies MUST be combined before they are applied to the metadata statement. Using the notation we have defined in , policies are combined starting with ES[i] and then adding the policies from ES[j] j=i-1,..,1 before applying the combined policy to the entity's metadata. After each combination, the policy for each parameter MUST adhere to the rules defined in .

The result of merging the values of two subset_of operators is the intersection of the operator values. The result of merging the values of two one_of operators is the intersection of the operator values. The result of merging the values of two superset_of operators is the union of the operator values. The result of merging the values of two add operators is the union of the values. Merging two value operators is NOT allowed unless the two operator values are equal. Merging two default operators is NOT allowed unless the two operator values are equal. If a superior has specified essential=true, then a subordinate cannot change that. If a superior has specified essential=false, then a subordinate is allowed to change that to essential=true. If a superior has not specified essential, then a subordinate can set essential to true or false.

Once combining the Metadata policies has been accomplished, the next step is to apply the combined policy to the metadata. Doing that, one follows these steps for each parameter in the policy. If there is a value operator in the policy, apply that and you are done. Add whatever value is specified in an add operator. If the parameter still has no value apply the default if there is one. Do the essential check. If essential is missing as an operator essential is to be treated as if set to false. If essential is defined to be true, then the claim MUST have a value by now. Otherwise applying the operator MUST fail. Do the other checks. Verified that the value is one_of or that the values are subset_of/superset_of. If the parameter values do not fall within the allowed boundaries, applying the operator MUST fail.

A federation's policy for RPs:

An organization's policy for RPs:

The combined metadata policy then becomes:

If applying policies to a metadata statement results in incorrect metadata, then such a metadata statement MUST be regarded as broken and MUST NOT be used.

There might be parties that want to extend the policy language defined here. If that happens then the rule is that if software compliant with this specification encounters a keyword it does not understand, it MUST ignore it unless it is listed in a policy_language_crit list, as is done for JWS header parameters with the crit parameter. If the policy language extension keyword is listed in the policy_language_crit list and not understood, then the metadata MUST be rejected.

The following is a non-normative example of a set of policies being applied to an RP's metadata.

The RP's metadata:

The federation's policy for RPs:

The organization's policy for RPs:

The metadata for the entity in question, after applying the policies above, would then become:

A constraint specification can contain the following claims: OPTIONAL. Integer. The maximum number of entity statements between this entity statement and the last entity statement in the trust chain. OPTIONAL. JSON object. Restriction on the entity identifiers of the entities below this entity. The behavior of this claim mimics what is defined in Section 4.2.1.10 in . Restrictions are defined in terms of permitted or excluded name subtrees. The following is a non-normative example of such a specification:

If a subordinate entity statement contains a constraint specification that is more restrictive than the one in effect, then the more restrictive constraint is in effect from here on. If a subordinate entity statement contains a constraint specification that is less restrictive than the one in effect, then it MUST be ignored.

The max_path_length constraint specifies the maximum number of entity statement a trust chain can have between the entity statement that contains the constraint specification and the leaf's entity statement. A max_path_length constraint of zero indicates that no entity statement MAY appear between this entity statement and the leaf entity statement. Where it appears, the max_path_length constraint MUST have a value that is greater than or equal to zero. Where max_path_length does not appear, no limit is imposed. Assuming that we have a trust chain with four entity statements: Leaf entity (LE) Intermediate 1 (I1) Intermediate 2 (I2) Trust Anchor (TA) Then the trust chain fulfills the constraints if: The TA specifies a max_path_length that is equal to or bigger than 2. TA specifies max_path_length of 2, I2 specifies max_path_length of 1, and I1 specifies no max_path_length constraint. Neither TA nor I2 specifies any max_path_length constraint while I1 specifies max_path_length of 0. The trust chain does not fulfill the constraints if: TA has specified max_path_length of 1.

The naming_constraints member specifies a namespace within which all subject entity identifiers in subordinate entity statements in a trust chain MUST be located. Restrictions are defined in terms of permitted or excluded name subtrees. Any name matching a restriction in the excluded claim is invalid regardless of information appearing in the permitted claim. The constraint MUST be specified as a fully qualified domain name and MAY specify a host or a domain. Examples would be "host.example.com" and ".example.com". When the constraint begins with a period, it MAY be expanded with one or more labels. That is, the constraint ".example.com" is satisfied by both host.example.com and my.host.example.com. However, the constraint ".example.com" is not satisfied by "example.com". When the constraint does not begin with a period, it specifies a host.

In this specification we use the US NSTIC definition: "A trustmark is used to indicate that a product or service provider has met the requirements of the Identity Ecosystem, as determined by an accreditation authority". Technically, trust marks as used by this specification are signed JWTs that represent a statement of conformance to a well-scoped set of trust and/or interoperability requirements. The trust marks are signed by a federation accredited authority. The validation of such a signed statement is performed in the same way that a self-signed entity statement is validated. Note that a federation MAY allow an entity to self-sign some trust marks.

These are the properties that can occur in a trust mark: REQUIRED. String. The issuer of the trust mark. REQUIRED. String. The entity this trust mark applies to. REQUIRED. String. An identifier of the trust mark. REQUIRED. Number. When this trust mark was issued. Expressed as Seconds Since the Epoch, per . OPTIONAL. String. An URL that points to a mark/logo that the subject is allowed to display to a user of the entity. OPTIONAL. Number. When this trust mark is not valid anymore. Expressed as Seconds Since the Epoch, per . If not present, it means that the trust mark is valid forever. OPTIONAL. String. URL that points to information connected to the issuance of this trust mark.

An entity SHOULD NOT try to validate a trust mark until it knows which trust anchors it wants to use. validating a trust mark follows the procedure set out in Note that the entity representing the accreditation authority MUST be immediately below the trust anchor. There cannot be any intermediate between it and the trust anchor.

An example of a self-signed certification mark:

An example of a third-party accreditation authority:

The configuration endpoint is found using the Well-Known URIs specification, with the suffix openid-federation. The scheme, host, and port are taken directly from the entity identifier combined with the following path: /.well-known/openid-federation. If the entity identifier contains a path, it is concatenated after /.well-known/openid-federation in the same manner that path components are concatenated to the well-known identifier in the OAuth 2.0 Authorization Server Metadata specification. Of course, in real multi-tenant deployments, in which the entity identifier might be of the form https://multi-tenant-service.example.com/my-tenant-identifier the tenant is very likely to not have control over the path https://multi-tenant-service.example.com/.well-known/openid-federation/my-tenant-identifier whereas it is very likely to have control over the path https://multi-tenant-service.example.com/my-tenant-identifier/.well-known/openid-federation. Therefore, if using the configuration endpoint at the URL with the tenant path after the well-known part fails, it is RECOMMENDED that callers retry at the URL with the tenant path before the well-known part (even though this violates ). Federation Entities SHOULD make an Entity Configuration Document available at the configuration endpoint. There is only one exception to this rule and that is for an RP that only does explicit registration. Since it posts the self-signed entity statement to the OP during client registration, the OP has everything it needs from the RP.

A federation Entity Configuration Document MUST be queried using an HTTP GET request at the previously specified path. The requesting party would make the following request to the Entity https://example.com to obtain its Configuration information:

The response is a self-signed Entity Statement, as described in . If the entity is an intermediate entity or a trust anchor, the response MUST contain metadata for a federation entity. A positive response is a signed entity statement, where the content type MUST be set to application/jose. In case of an error, the response will be a JSON object, the content type MUST be set to application/json and the error response uses the applicable HTTP status code value. The following is a non-normative example response from an intermediate entity, before serialization and adding a signature:

All entities that are expected to publish entity statements about other entities MUST expose a Federation API endpoint. The federation API endpoint of an entity can be found in the configuration response as described in or by other means. The Federation API is an HTTPS API that MAY support multiple operations. Fetching entity statements is one of the operations, and the only one that all Federation API endpoints are REQUIRED to support. All the other operations are OPTIONAL. The list of defined operations MAY be extended in the future. While all operations on the federation API endpoint make use of a GET request, other operations MAY choose to use other HTTP methods. If the operation parameter is left out, it is treated as a fetch entity statements request. Unless otherwise mentioned or agreed upon, requests to the federation API do not need to be authenticated.

Fetching entity statements is performed to collect entity statements one by one to gather trust chains. To fetch an entity statement, an entity needs to know the identifier of the entity to ask (the issuer), the federation API endpoint of that entity and the identifier of the entity that you want the statement to be about (the subject).

The request MUST be an HTTP request using the GET method and the https scheme to a resolved federation API endpoint with the following query string parameters: OPTIONAL. If not present, MUST be treated as fetch. REQUIRED. The entity identifier of the issuer from which you want an entity statement issued. Because of the normalization of the URL, multiple issuers MAY resolve to a shared federation API. This parameter makes it explicit exactly which issuer we want entity statements from. OPTIONAL. The entity identifier of the subject for which you would like an entity statement issued. If this parameter is left out, it is considered to be the same as the issuer and would indicate a request for a self-issued statement. OPTIONAL. The entity identifier of the requester. If the aud parameter is present in the request, the aud claim SHOULD be present in the entity statement response and take exactly that value.

The following is a non-normative example of an API request for an entity statement:

A positive response is a signed entity statement where the content type MUST be set to application/jose. If it is a negative response, it will be a JSON object and the content type MUST be set to application/json. See more about error responses in .

The following is a non-normative example of a response, before serialization and adding a signature:

An entity MAY use the trust negotiation operation to fetch resolved metadata about itself as seen/trusted by a remote peer. The result may, for instance, tell an RP what operations, scopes and claims an OP would allow the RP to use if a specific trust anchor was used.

The request MUST be an HTTP request using the GET method and the https scheme to a resolved federation API endpoint with the following query string parameters: REQUIRED. MUST be set to resolve_metadata. REQUIRED. The entity identifier of the entity whose metadata are requested. Because of the normalization of the URL, multiple entity identifiers may resolve to a shared federation API. This parameter makes it explicit exactly which entity is expected. REQUIRED. The entity identifier of the entity the information is requested for. This MUST be a leaf entity. REQUIRED. The metadata type to resolve. In this document, we use the metadata types listed in . REQUIRED. The trust anchor that the remote peer MUST use when resolving the metadata. The value is an entity identifier.

The following is a non-normative example of an API request for trust negotiation:

The response is a metadata statement that is the result of applying the metadata policies in the trust chain on the entity's metadata.

The following is a non-normative example of a response:

An entity MAY query another entity for a list of all the entities immediately subordinate to that entity and about which that entity is prepared to issue statements about. (In some cases, this MAY be a very large list.)

The request MUST be an HTTP request using the GET method and the https scheme to a resolved federation API endpoint with the following query string parameters: REQUIRED. MUST be set to listing. REQUIRED. The entity identifier of the entity from which an entity listing is requested. Because of the normalization of the URL, multiple entity identifiers may resolve to a shared federation API. This parameter makes it explicit exactly which entity is expected. OPTIONAL. If left out, the result should include both leaf entities and intermediate nodes. If set to true, the response SHOULD contain only leaf entities. If set to false, the response SHOULD contain only intermediate nodes.

The following is a non-normative example of an API request for trust negotiation:

The response MUST contain an JSON list with the known entity identifiers.

The following is a non-normative example of a response:

If the request was malformed, or some error occurred during processing of the request, the following standardized error format SHOULD be used regardless of the operation specified. The HTTP response code MUST be something in 400/500-range, giving an indication of the type of error. The response body MUST be a JSON object containing the claims below and the content type MUST be set to application/json. REQUIRED. The operation of the request. REQUIRED. The error code. REQUIRED. A human-readable short text describing the error.

The following is a non-normative example of an error response:

An entity (e.g., the Consumer) that wants to establish trust with a remote peer, MUST have the remote peer's entity identifier and a list of entity identifiers of trust anchors together with the public version of their signing keys. The Consumer will first have to fetch sufficient entity statements to establish at least one chain of trust from the remote peer to one or more of the configured trust anchors. After that the entity MUST validate the trust chains independently, and -- if there are multiple valid trust chains and if the application demands it -- choose one.

Depending on the circumstances, the Consumer MAY either be handed the remote peer's self-issued entity statement, or it may have to fetch it by itself. If it needs to fetch it, it will use the process described in with both iss and sub containing the entity identifier of the remote peer. The next step is to iterate through the list of intermediates listed in authority_hints, ignoring the authority hints that end in an unknown trust anchor, requesting an entity statement about the remote peer from each of the intermediates. If the received entity statement contains an authority hint this process is repeated. This time with the iss set to the intermediate's entity identifier and the sub to be the iss of the previous query. The Consumer SHOULD NOT attempt to fetch entity statements it already has fetched during this process (loop prevention). A successful operation will return one or more lists of entity statements. Each of the lists terminating in a self-signed entity statement is issued by a trust anchor. If there is no path from the remote peer to at least one of the trusted trust anchors, then the list will be empty and there is no way of establishing trust in the remote peer's information. How the Consumer deals with this is out of scope for this specification.

As described in , a trust chain consists of an ordered list of entity statements. So whichever way the Consumer has acquired the set of entity statements, it MUST now verify that it is a proper trust chain using the rules laid out in that section. To validate the chain, the following MUST be done: For each entity statement ES[j] j=i,..,0: Verify that the statement contains all the required claims. Verify that iat has a value in the past. Verify that exp has a value that is in the future. For j=0 verify that iss == sub. For j=0,...,i-1: Verify that ES[j]['iss'] == ES[j+1]['sub'] For j=0,...,i-1: Verify the signature of ES[j] using a public key carried in ES[j+1]['jwks']. For j == 0 verify the signature of ES[0] using a public key carried in ES[0]['jwks']. For j == i: verify that a) the issuer matches the configured identifier of a trust anchor and b) its signature is valid with the likewise configured public key of said trust anchor. Verifying the signature is a much more expensive operation then verifying the correctness of the statement and the timestamps. An implementer MAY therefor chose to not verify the signature until all the other checks have been done. Consumers MAY cache Entity Statements or signature verification results for a given time until they expire . Note that the second bullet point means that, at each step in the trust chain resolution, it MUST be verified that the signing JWK is also present in the jwks statement claim issued by the superior.

If multiple valid trust chains are found, the Consumer will need to decide on which one to use. One simple rule would be to prefer a shorter chain over a longer one. Consumers MAY follow other rules according to local policy.

Each entity statement in a trust chain is signed and MUST have an expiration time (exp) set. The expiration time of the whole trust chain is set to the minimum value of exp within the chain.

This specification allows for a smooth process of updating metadata and public keys. As described above in , each trust chain has an expiration time. A consumer of metadata using this specification MUST support refreshing a trust chain when it expires. How often a consumer SHOULD re-evaluate the trust chain depends on how quickly the consumer wants to find out that something has changed in the trust chain.

If a leaf entity publishes its public keys in the metadata part using jwks, setting an expiration time on the self-signed entity statement can be used to control how often the receiving entity is fetching an updated version of the public key.

A trust anchor MUST publish a self-signed entity statement about itself. The trust anchor SHOULD set a reasonable expiration time on that statement, such that the consumers will re-fetch the entity statement at reasonable intervals. If the trust anchor wants to roll over its signing keys it would have to: Add the new keys to the jwks representing the trust anchors signing keys. Keep signing the entity statement using the old keys for a long enough time period to allow all subordinates to have gotten access to the new keys. Switch to signing with the new keys. After a reasonable time period remove the old keys. What is regarded as a reasonable time is dependent on the security profile and risk assessment of the trust anchor. It MUST be taken into consideration that clients MAY have manually configured public keys as part of their configuration.

Since the consumers are expected to check the trust chain at regular, reasonably frequent times, this specification does not specify a standard revocation process. Specific federations MAY make a different choice and will then have to add such a process.

This section describes how the trust framework in this specification is used to establish trust between an RP and an OP that have no explicit configuration or registration in advance. There are two alternative approaches to establish trust between an RP and an OP, which we call automatic and explicit registration. Members of a federation or a community SHOULD agree upon which one to use. While implementations should support both methods, deployments MAY choose to disable the use of one of them. Independent of whether the RP uses automatic or explicit registration, the way that the RP learns about the OP is the same. It will use the procedure that is described in .

Automatic registration allows an RP to send Authorization Requests to an OP without first registering with the OP. It basically works by the OP using the Client ID in the request to find the RP's metadata using the process outlined in and then verifies that the RP is in control of a private key that is a companion to one of the public keys the RP published through its metadata. For automatic registration to work a number of things MUST be valid: The Client ID of the RP MUST be set to be identical to the RP entity identifier. Without a registration process, the RP does not have a client secret. Instead, the automatic registration model requires the RP to make use of asymmetric cryptography. Basically, the RP must prove that it has control of the RP's private keys. The Client ID MUST be a URL from which the OP can fetch the RP's self-signed entity statement using the process described in . The OP MUST publish that it supports a request authentication method using the metadata claim request_authentication_methods_supported.

The Authentication Request is performed by passing a Request Object by value as described in Section 6.1 in OpenID Connect Core 1.0 or using pushed authorization as described in Pushed Authorization Requests.

In the case where a Request Object is used, the value of the request parameter is a JWT whose Claims are the request parameters specified in Section 3.1.2 in OpenID Connect Core 1.0. The JWT MUST be signed and MAY be encrypted. The following restrictions apply to the JWT: REQUIRED. The Audience (aud) MUST be the URL of the Authorization Server's Authorization Endpoint. REQUIRED. The claim iss MUST contain the client identifier. MUST NOT be present. This together with the value of aud SHOULD make reuse of the statement for private_key_jwt client authentication not feasible. REQUIRED. JWT ID. A unique identifier for the JWT, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties; any such negotiation is beyond the scope of this specification. REQUIRED. Expiration time on or after which the JWT MUST NOT be accepted for processing. OPTIONAL. Time at which the JWT was issued.

The following is a non-normative example of the Claims in a Request Object before base64url encoding and signing:

The following is a non-normative example of an Authorization Request using the request parameter (with line wraps within values for display purposes only):

When the OP receives an incoming Authentication Request, the OP supports OpenID Connect Federation, the incoming Client ID is a valid URL, and the OP does not have the Client ID registered as a known client, then the OP SHOULD try to resolve and fetch trust chains starting with the RP's entity statement as described in . The OP MUST then validate the possible trust chains, as described in , and resolve the RP metadata with type openid_relying_party. The OP SHOULD furthermore consider the resolved metadata of the RP, and verify that it complies with the client metadata specification in OpenID Connect Dynamic Client Registration 1.0. Once the OP has the RP's metadata, it can verify that the client was actually the one sending the Authorization Request by verifying the signature of the Request Object using the key material the client published through its metadata.

Pushed Authorization provides an interoperable way to push the payload of a Request Object directly to the AS in exchange for a request_uri. When it comes to request authentication, the applicable methods are three: Using a JWT for Client authentication as described for private_key_jwt in Section 9 of OpenID Connect Core 1.0. mTLS as described in Section 2.2 of based on self-signed certificates. In this case the self-signed certificate MUST be present as the value of an x5c claim for one key in the JWK Set describing the RP's keys. mTLS as described in Section 2.1 of based on public key infrastructure (PKI). Note that if mTLS is used, TLS client authentication MUST be configured and, in case of self-signed certificates, the server must omit trust chain validation (optional_no_ca). Using the example above, a request could look like this:

There are three different paths the OP MUST follow when processing the Authentication Request depending on which request authentication method that was used. It all starts the same though. When the OP receives an incoming Authentication Request, the OP supports OpenID Connect Federation, the incoming Client ID is a valid URL, the OP does not have the Client ID registered as a known client and the OP supports the request authentication method used then the OP SHOULD try to resolve and fetch trust chains starting with the RP's entity statement as described in . The OP SHOULD validate the possible trust chains, as described in , and resolve the RP metadata with type openid_relying_party. The OP SHOULD consider the resolved metadata of the RP, and verify that it complies with the client metadata specification in OpenID Connect Dynamic Client Registration 1.0. Once the OP has the RP's metadata, it can verify the client. This is where it diverges depending on which client authentication method was used. If this method is used, then the OP will try to verify the signature of the signed JWT using the key material published by the RP in its metadata. If the authentication is successful, then the registration is regarded as correct. If mTLS is used and the certificate used was not self-signed, then the Subject Alternative Name of the certificate MUST match the entity identifier of the RP. If mTLS is used and the certificate used is a self-signed certificate, then the certificate MUST be present as the value of an x5c claim for one key in the JWK Set describing the RP's keys.

If the OP fails to establish trust with the RP, it SHOULD use an appropriate error code, and an error_description that aids the RP to understand what is wrong. In addition to the error codes defined in Section 3.1.2.6 of OpenID Connect Core, this specification also defines the following error codes: No trusted trust anchor could be found. Trust chain validation failed.

The following is a non-normative example error response:

This method involves performing an explicit registration of a new client the first time an RP interacts with an OP using something that basically follows the steps in OpenID Connect Dynamic Client Registration 1.0 but where the client registration request is a signed entity statement.

The OP MUST support OpenID Dynamic Client Registration as extended by this specification. This is signaled by having the claim federation_registration_endpoint in the OP's metadata. Given that the OP supports explicit registration, the RP progresses as follows: Once it has the list of acceptable trust chains for the OP, it MUST choose the subset it wants to progress with. The subset can be as small as one trust chain, but it can also contain more than one. Based on the trust anchors referenced in the subset of trust chains, the RP will choose a set of authority_hints from its own set that terminate in those trust anchors. The RP will now construct a self-signed entity statement where the metadata statement chosen is influenced by the OPs metadata and the authority_hints included are picked by the process described above. Note that the aud claim in the entity statement is REQUIRED in this case and MUST be set to the OP issuer identifier. The entity statement is sent, using POST, to the federation_registration_endpoint defined in this document. The content type MUST be set to application/jose.

The trust chains MUST be constructed using the received entity statement. After the OP receives the request, it collects and evaluates the trust chains starting with the authority_hints in the registration request. After it has verified at least one trust chain it MUST verify that the signature on the received registration request is correct. If it finds more than one acceptable trust chain, it MUST choose one trust anchor from those chains as the one it will proceed with. At this point, if there already exists a client registration under the same entity identifier then that registration MUST be regarded as invalid. Note that key material from the previous registration SHOULD be kept to allow verifying a signature on, or decrypting archived data. The OP will now construct a metadata policy that, if applied to the RP's metadata statement, will result in metadata that the OP finds acceptable. Note that the Client ID the OP chooses does not have to be the same as the entity identifier of the RP. To the entity statement it will add a trust_anchor_id claim, containing the trust anchor chosen above. It will sign and return the registration response (a signed entity statement) to the RP.

The RP verifies the correctness of the received entity statement, making sure that the trust chains starting at the authority_hints terminate in trust anchors that were referenced in the entity statement it sent to the OP. The RP MUST NOT apply metadata policies from the trust chains that the OP provides because those are not valid for the RP's metadata. The RP MUST apply policies to the metadata using one of its own trust chains that ends in the trust anchor that the OP chose. Once it has applied those policies, it can then apply the policy returned from the OP. When it has applied all the metadata policies to its metadata statement, it then stores the result and can continue communicating with the OP using the agreed-upon metadata. At this point the RP also knows which trust chain it should use when evaluating the OP's metadata. It can therefore apply the metadata policies on the OP's metadata using the relevant trust chain and store the result as the OPs metadata. If the RP does not accept the received entity statement for some reason, then it has the choice to restart the registration process or to give up.

A client registration using this specification is not expected to be valid forever. The entity statements exchanged all have expiration times, which means that the registration will eventually time out. An OP can also, for administrative reasons, decide that a client registration is not valid anymore. An example of this could be that the OP leaves the federation in use.

At regular intervals, the RP MUST: Starting with the OP's entity statement, resolve and verify the trust chains it chooses to use when constructing the registration request. If those trust chains do not exist anymore or do not verify, then the registration SHOULD be regarded as invalid and a new registration process SHOULD be started. If the OP's entity statement was properly formed the RP must now verify that the entity statement it received about itself from the OP is still valid. Again, if that is not the case the registration SHOULD be regarded as invalid and a new registration process SHOULD be started. What is regarded as reasonable intervals will depend on federation policies and risk assessment by the maintainer of the RP.

At regular intervals, the OP MUST: If the signature on the registration request has expired it MUST mark the registration as invalid and demand that the RP MUST re-register. Else starting with the RP's client registration request, the OP MUST verify that there still is a valid trust chain terminating in the trust anchor the OP chose during the registration process.

An OP MUST NOT assign an expiration time to an RP's registration that is later than the trust chain's expiration time.

TBD Register federation_types_supported for OP metadata with initial values automatic and explicit. TBD Register federation_type for RP registration metadata. TBD Register federation_registration_endpoint for the OP metadata.

Some of the interfaces defined in this specification could be used for Denial of Service attacks (DOS), most notably, Entity Listings () and automatic client registration (). If you plan to provide these interfaces as a service, you should consider applying normal defense methods, such as those described in .

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Let us assume the following: The project LIGO would like to offer access to its wiki to all OPs in EduGAIN. LIGO is registered to the InCommon federation.

The players

Both SWAMID and InCommon are identity federations in their own right. They also have in common that they both are members of the EduGAIN federation. SWAMID and InCommon are different in how they register entities. SWAMID registers organizations and lets the organizations register entities that belong to the organization, while InCommon registers all entities directly and not beneath any organization entity. Hence the differences in depth in the federations. Let us assume a researcher from Umeå University would like to login at the LIGO Wiki. At the Wiki, the researcher will use some kind of discovery service to find the home identity provider (op.umu.se) Once the RP-part of the Wiki knows which OP it SHOULD talk to it has to find out a couple of things about the OP. All if those things can be found in the metadata. But finding the metadata is not enough; the RP also has to trust the metadata. Let us start with discovering Provider information.

Metadata discovery is a sequence of steps that starts with the RP fetching the self-signed entity statement of the leaf (in this case https://op.umu.se) using the process defined in . What follows thereafter is this sequence of steps: Pick out the immediate superior entities using the authority hints Fetch the configuration for each such entity. This uses the process defined in Using the federation API endpoint of the superiors do a fetch request on the endpoint asking for information about the subordinate entity. How many times this has to be repeated depends on the depth of the federation. What follows below is the result of each step the RP has to take to find the OP's metadata using the federation setup described above. When building the trust chain, the entity statements issued by a superior about its subordinate are used together with the self-signed entity statement issued by the leaf. The self-signed entity statement concerning intermediates are not part of the trust chain.

The LIGO WIKI RP fetches the self-signed entity statement from the OP (op.umu.se) using the process defined in .

The result is this entity statement.

The authority_hints points to the intermediate https://umu.se. So that is the next step. This entity statement is the first link in the trust chain.

The LIGO RP fetches the self-signed entity statement from "https://umu.se" using the process defined in . The request will look like this:

And the GET will return:

The only piece of information that is used from this entity statement is the federation_api_endpoint, which is used in the next step.

The RP uses the federation API and the "fetch" command as defined in to fetch information about "https://op.umu.se" from the API endpoint published in https://umu.se's configuration. The request will look like this:

and the result is this:

This is the second link in the trust chain. Notable here is that this path leads to two trust anchors using the same next step ("https://swamid.se").

The LIGO Wiki RP fetches the self-signed entity statement from "https://swamid.se" using the process defined in . The request will look like this:

And the GET will return:

The only piece of information that is used from this entity statement is the federation_api_endpoint, which is used in the next step.

The LIGO Wiki RP uses the federation API and the "fetch" command as defined in to fetch information about "https://umu.se" from the API endpoint published in https://swamid.se's configuration. The request will look like this:

and the result is this:

This is the third link in the trust chain. If we assume that the issuer of this entity statement is not in the list of trust anchors the LIGO Wiki RP has access to we have to go one step further.

RP fetches the self-signed entity statement from "https://edugain.geant.org" using the process defined in . The request will look like this:

And the GET will return:

Again, the only thing we need is the federation_api_endpoint. As described in , note SHOULD also be taken to jwks as the trust anchor MAY be performing a key rollover.

The LIGO Wiki RP uses the federation API and the "fetch" command as defined in to fetch information about "https://swamid.se" from the API endpoint published in https://edugain.geant.org's configuration. The request will look like this:

and the result is this:

If we assume that the issuer of this statement appears in the list of trust anchors the LIGO Wiki RP has access to this would be the fourth and final entity statement in the trust chain. We now have the whole chain from the self-signed entity statement of the leaf up until the last one that is issued by a trust anchor. All in all, we have: Self-signed entity statement by the leaf (https://op.umu.se) Statement issued by https://umu.se about https://op.umu.se Statement issued by https://swamid.se about https://umu.se Statement issued by https://edugain.geant.org about https://swamid.se We also have the self-signed entity statements from https://umu.se, https://swamid.se and https://edugain.geant.org about themselves but those are not used in the trust chain verification. Using the public keys of the trust anchor that the LIGO Wiki RP has been provided with in some secure out-of-band way, it can now verify the trust chain as described in .

Having verified the chain, the LIGO Wiki RP can proceed with the next step. Combining the metadata policies from the tree entity statements we have by a superior about its subordinate and applying the combined policy to the metadata statement that the leaf entity presented, we get:

We have now reached the end of the Provider Discovery process.

As described in , there are two ways which can be used to do client registration: No negotiation between the RP and the OP is made regarding what features the client SHOULD use in future communication are done. The RP's published metadata filtered by the chosen trust chain's metadata policies defines the metadata that is to be used. The RP will access the federation_registration_endpoint, which provides the metadata for the RP to use. The OP MAY return a metadata policy that adds restrictions over and above what the trust chain already has defined.

The LIGO Wiki RP does not do any registration but goes directly to sending an Authentication Request. Here is an example of such an Authentication Request:

The OP receiving this Authentication Request will, unless the RP is already registered, start to dynamically fetch and establish trust with the RP.

The OP needs to establish a trust chain for the RP (wiki.ligo.org). The OP in this example is configured with public keys of two federations: https://edugain.geant.org https://swamid.se The OP starts to resolve metadata for the client identifier https://wiki.ligo.org by fetching the self-issued entity statement using the process described in . The process is the same as described in and will result in a trust chain with the following entity statements: Self-signed entity statement by the leaf https://wiki.ligo.org Statement issued by https://incommon.org about https://wiki.ligo.org Statement issued by https://edugain.geant.org about https://incommon.org

Using the public keys of the trust anchor that the LIGO Wiki RP has been provided with in some secure out-of-band way, it can now verify the trust chain as described in . We will not list the complete entity statements but only the metadata and metadata_policy parts. There are two metadata policies:

If you combine these and apply them to the metadata for wiki.ligo.org :

You will get

Having that, the registration is done, and the OP MUST now use the keys found at the URL specified in jwks_uri to verify the signature on the Request Object in the Authentication Request.

Here the LIGO Wiki RP sends a client registration request to the federation_registration_endpoint of the OP (op.umu.se). What it sends is a self-signed entity statement. Once the OP has the entity statement, it proceeds with the same sequence of steps as laid out in . The OP will end up with the same RP metadata as was described in , but what it now can do is return a metadata policy that it wants to be applied to the RP's metadata. This metadata policy will be combined with the trust chain's combined metadata policy before being applied to the RP's metadata. If we assume that the OP does not support refresh tokens, it MAY want to add a metadata policy that says:

Thus, the entity statement returned by the OP to the RP MAY look like this:

And the resulting metadata used by the RP could look like:

Copyright (c) 2021 The OpenID Foundation. The OpenID Foundation (OIDF) grants to any Contributor, developer, implementer, or other interested party a non-exclusive, royalty free, worldwide copyright license to reproduce, prepare derivative works from, distribute, perform and display, this Implementers Draft or Final Specification solely for the purposes of (i) developing specifications, and (ii) implementing Implementers Drafts and Final Specifications based on such documents, provided that attribution be made to the OIDF as the source of the material, but that such attribution does not indicate an endorsement by the OIDF. The technology described in this specification was made available from contributions from various sources, including members of the OpenID Foundation and others. Although the OpenID Foundation has taken steps to help ensure that the technology is available for distribution, it takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this specification or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any independent effort to identify any such rights. The OpenID Foundation and the contributors to this specification make no (and hereby expressly disclaim any) warranties (express, implied, or otherwise), including implied warranties of merchantability, non-infringement, fitness for a particular purpose, or title, related to this specification, and the entire risk as to implementing this specification is assumed by the implementer. The OpenID Intellectual Property Rights policy requires contributors to offer a patent promise not to assert certain patent claims against other contributors and against implementers. The OpenID Foundation invites any interested party to bring to its attention any copyrights, patents, patent applications, or other proprietary rights that MAY cover technology that MAY be required to practice this specification.

The authors wish to acknowledge the contributions of the following individuals and organizations to this specification: Vladimir Dzhuvinov, Heather Flanagan, Jouke Roorda, Misha Salle, Marcos Sanz, Peter Schober, Michael Schwartz, and the JRA3T3 task force of GEANT4-2.

The following open issues remain to be addressed in this specification. The representation for RPs that are native applications needs to be defined. How are federation operator keys retrieved? A mechanism is needed for key rotation of federation operator keys for long-term security and maintainability of federations. A mechanism MAY be needed for bounding key lifetimes. Discuss that Key IDs MAY be chosen as the JWK Thumbprint [RFC 7638] of the key. Discuss localization of human-readable strings. SAML2 as used in Research and Education federations uses post-/prefix matching on metadata in some cases. We might need something similar or just use regular expressions. Define the relationship between trust anchors and Federation Operators, as people will expect to find the Federation Operator term in the specification. Add a diagram showing the relationships between FOs, orgs, sub-orgs, and leaf entities.

[[ To be removed from the final specification ]] -16 Added Security Considerations section on Denial of Service attacks. -15 Added signed_jwks_uri, which had be lost somewhere along the road. -14 Rewrote the federation policy section. What previously was referred to as client authentication in connection with automatic client registration is now changed to be request authentication. Made a distinction between parameters and claims. Corrected the description of the intended behavior when essential is absent. -13 Added 'trust_marks' as a parameter in the entity statement. An RP's self-signed entity statement MUST have the OP's issuer identifier as the value of 'aud'. Added RS256 as default signing algorithm for entity statements. Specified that the value of 'aud' in the entity statement use in automatic client registration MUST have the ASs authorization endpoint URL as value. Also the 'sub' claim MUST NOT be present. Separating the usage of merge and combine as proposed by Vladimir Dzhuvinov in Bitbucket issue #1157. An RP doing only explicit client registration are not required to publish and support a .well-known/openid-federation endpoint. Every key in a JWK Set in an entity statement MUST have a kid. -12 Made JWK Set OPTIONAL in an entity statement returned by OP as response of an explicit client registration Renamed entity type to client registration type. Added more text describing client_registration_auth_methods_supported. Made "Processing the Authentication Request" into two separate sections: one for Authentication Request and one for Pushed Authorization Request. Added example of URLs to some examples in the appendix. Changed the automatic client registration example in the appendix to use Request Object instead of a client_assertion. -11 Added section on trust marks. Clarified private_key_jwt usage in the authentication request. Fixed Bitbucket issues #1150 and #1155 by Vladimir Dzhuvinov. Fixed some examples to make them syntactically correct. -10 Incorporated additional review feedback from Marcos Sanz. The primary change was moving constraints to their own section of the entity statement. -09 Incorporated review feedback from Marcos Sanz. Major changes were as follows. Separated entity configuration discovery from operations provided by the federation API. Defined new authentication error codes. Also incorporated review feedback from Michael B. Jones. -08 Incorporated review feedback from Michael B. Jones. Major changes were as follows. Deleted sub_is_leaf entity statement since it was redundant. Added federation_type RP registration metadata value and federation_types_supported OP metadata value. Deleted openid_discovery metadata type identifier since its purpose is already served by openid_provider. Entity identifier paths are now included when using the Federation API, enabling use in multi-tenant deployments sharing a common domain name. Renamed sub_is_leaf to is_leaf in the Entity Listings Request operation parameters. Added crit and policy_language_crit, enabling control over which entity statement and policy language extensions MUST be understood and processed. Renamed openid_client to openid_relying_party. Renamed oauth_service to oauth_authorization_server. Renamed implicit registration to automatic registration to avoid naming confusion with the implicit grant type. Renamed op to operation to avoid naming confusion with the use of "OP" as an acronym for "OpenID Provider". Renamed url to uri in several identifiers. Restored Open Issues appendix. Corrected document formatting issues. -07 Split metadata into metadata and metadata_policy Updated example -06 Some rewrites Added example of explicit client registration -05 A major rewrite. -04 Changed client metadata names scopes to rp_scopes and claims to rp_claims. Added Open Issues appendix. Added additional references. Editorial improvements. Added standard Notices section, which is present in all OpenID specifications.