The MITRE Corporation

kburgin@mitre.org

The MITRE Corporation

tclancy@mitre.org

OpenID iGov Working Group The OAuth 2.0 protocol framework defines a mechanism to allow a resource owner to delegate access to a protected resource for a client application. This specification profiles the OAuth 2.0 protocol framework to increase baseline security, provide greater interoperability, and structure deployments in a manner specifically applicable, but not limited to consumer-to-government deployments.

This document profiles the OAuth 2.0 web authorization framework for use in the context of securing web-facing application programming interfaces (APIs), particularly Representational State Transfer (RESTful) APIs. The OAuth 2.0 specifications accommodate a wide range of implementations with varying security and usability considerations, across different types of software clients. The OAuth 2.0 client, protected resource, and authorization server profiles defined in this document serve two purposes: Define a mandatory baseline set of security controls suitable for a wide range of government use cases, while maintaining reasonable ease of implementation and functionality Identify optional, advanced security controls for sensitive use cases where increased risk justifies more stringent controls.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 . All uses of JSON Web Signature (JWS) and JSON Web Encryption (JWE) data structures in this specification utilize the JWS Compact Serialization or the JWE Compact Serialization; the JWS JSON Serialization and the JWE JSON Serialization are not used.

This specification uses the terms "Access Token", "Authorization Code", "Authorization Endpoint", "Authorization Grant", "Authorization Server", "Client", "Client Authentication", "Client Identifier", "Client Secret", "Grant Type", "Protected Resource", "Redirection URI", "Refresh Token", "Resource Owner", "Resource Server", "Response Type", and "Token Endpoint" defined by OAuth 2.0 , the terms "Claim Name", "Claim Value", and "JSON Web Token (JWT)" defined by JSON Web Token (JWT) , and the terms defined by OpenID Connect Core 1.0 .

This specification defines requirements for the following components: OAuth 2.0 clients. OAuth 2.0 authorization servers. OAuth 2.0 protected resources. The specification also defines features for interaction between these components: Client to authorization server. Protected resource to authorization server. When an iGov-compliant component is interacting with other iGov-compliant components, in any valid combination, all components MUST fully conform to the features and requirements of this specification. All interaction with non-iGov components is outside the scope of this specification. An iGov-compliant OAuth 2.0 authorization server MUST support all features as described in this specification. A general-purpose authorization server MAY support additional features for use with non-iGov clients and protected resources. An iGov-compliant OAuth 2.0 client MUST use all functions as described in this specification. A general-purpose client library MAY support additional features for use with non-iGov authorization servers and protected resources. An iGov-compliant OAuth 2.0 protected resource MUST use all functions as described in this specification. A general-purpose protected resource library MAY support additional features for use with non-iGov authorization servers and clients.

All network connections MUST be made using TLS 1.3 or above. Each originator of a TLS connection MUST verify the destination's certificate. Additionally, the following four TLS 1.2 cipher suites MAY be used: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 Implementers of this profile SHOULD monitor the progress of specifications of post-quantum cryptography for TLS implementations. Implementers MAY adopt a cipher suite not included in BCP195 when post quantum safety is required if the cipher suite is supported in the implementation environment. An example of an emerging PQ cipher suite that is broadly supported at the time of writing is X25519MLKEM768, specified by Post-quantum Hybrid Key Exchange with ML-KEM in the Internet Key Exchange Protocol Version 2 (IKEv2). For the authorization_endpoint, the authorization server MAY allow additional cipher suites that are permitted by the latest version of BCP195, if necessary to allow sufficient interoperability with users' web browsers or as required by local regulations. NOTE: Permitted cipher suites are those listed in BCP195 that do not explicitly say MUST NOT use. Endpoints for use by web browsers MUST use mechanisms to ensure that connections cannot be downgraded using TLS Stripping attacks. Protected resources MAY implement an HTTP Strict Transport Security policy as defined in HTTP Strict Transport Security (HSTS) to mitigate these attacks. Protected resources SHOULD consider registering web domain names with browsers that offer browser-side ("preload") HSTS policy enforcement to further mitigate TLS downgrade attacks.

OAuth defines two client types, based on their ability to authenticate securely with the authorization server Clients that have credentials with the authorization server. Clients without credentials. Public client use cases are out of scope for this profile.

This specification has been designed around the following client use cases: A web application is a client running on a web server. Resource owners access the client via an HTML user interface rendered in a user agent on the device used by the resource owner. The client credentials as well as any access tokens issued to the client are stored on the web server and are not exposed to or accessible by the resource owner. In this use case, web applications are confidential clients and in-scope for this profile. A native application is a client installed and executed on the device used by the resource owner. Protocol data and credentials are accessible to the resource owner. It is assumed that any client authentication credentials included in the application can be extracted. Dynamically issued access tokens and refresh tokens can receive an acceptable level of protection. On some platforms, these credentials are protected from other applications residing on the same device. In this use case, native applications are public clients and out of scope for this profile. However, best current practices for native applications are detailed in OAuth 2.0 for Native Apps. In this use case, native applications are public clients. A browser-based application is a client in which the client code is downloaded from a web server and executes within a user agent (e.g., web browser) on the device used by the resource owner. Protocol data and credentials are easily accessible (and often visible) to the resource owner. If such applications wish to use client credentials, it is recommended to utilize the backend for frontend pattern. Since such applications reside within the user agent, they can make seamless use of the user agent capabilities when requesting authorization. In this use case, browser-based applications are public clients and out of scope for this profile. However, best current practices are detailed in OAuth 2.0 for Browser-Based Applications. This profile establishes requirements that can only be met by confidential clients. Government implementers with public client use cases are encouraged to consult the best practices identified above for those use cases.

All clients MUST register with the authorization server. For client software that may be installed on multiple client instances, each client instance MAY receive a unique client identifier from the authorization server. Client registration MAY be completed by either out-of-band configuration or using the Dynamic Client Registration Protocol. If a client uses mTLS for client authentication or to sender-constrain tokens, the client MUST include the tls_client_certificate_bound_access_tokens parameter in its registration metadata. If a client uses DPoP to sender constrain tokens, the client MUST include the dpop_bound_access_tokens parameter in its registration metadata. Clients using mTLS for client authentication or to sender-constrain tokens MUST register their TLS certificate's subject DN with the authorization server. Clients using self-signed certificate option are not guaranteed uniqueness of their certificate fingerprint.

Clients using the authorization code grant type MUST register their full redirect URIs. Clients MUST protect the values passed back to its redirect URI by ensuring that the redirect URI is one of the following: Hosted on a website with Transport Layer Security (TLS) protection (a Hypertext Transfer Protocol - Secure (HTTPS) URI) Hosted on a client-specific non-remote-protocol URI scheme (e.g., myapp://) Clients MUST use a unique redirect URI for each logical authorization server. Clients MUST NOT forward values passed back to their redirect URIs to other arbitrary or user-provided URIs (a practice known as an "open redirector"). Refer to Best Current Practice for OAuth 2.0 Security Section 2.4.1 for additional guidance on implementation of edge cases.

While a bearer token can be used by anyone in possession of the token, a sender-constrained token is bound to a particular symmetric or asymmetric key issued to, or already possessed by, the client. The association of the key to the token is also communicated to the protected resource. When the client presents the token to the protected resource, it is also required to demonstrate possession of the corresponding key. As described in Best Current Practice for OAuth 2.0 Security, sender-constrained tokens could prevent a number of attacks on OAuth that entail the misuse of stolen and leaked access tokens by unauthorized parties. The attacker would need to obtain the legitimate client's cryptographic key along with the access token to gain access to protected resources. All clients MUST use proof of possession to sender-constrain access tokens using either OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens or OAuth 2.0 Demonstrating Proof of Possession (DPoP).

Clients SHOULD support the mechanism specified in OAuth 2.0 Step Up Authentication Challenge Protocol" to communicate authentication context and implement interoperable step up authentication. This profile acknowledges government use cases will likely operate within an ecosystem of authentication methods of highly variable security value for the foreseeable future by imposing requirements to enable protected resources with basic capabilities to communicate requirements for authentication strength and recency to supporting authorization clients and servers, as well as the capability to enforce access policies using access tokens augmented with the strength and recency of the authentication event that led to the issuance of each specific access token. This profile leverages the supporting server metadata, request, token claims and values, and error messages from OAuth 2.0 Step Up Authentication Challenge Protocol and OpenID Connect Core 1.0. Digital identity policies and semantic mappings to string values are necessary for implementation but are out of scope for this profile. OAuth 2.0 MUST NOT be used as an authentication protocol. Use of the International Government Assurance Profile (iGov) for OpenID Connect 1.0 is RECOMMENDED to provide the identity authentication layer for iGov OAuth 2.0 delegated access use cases.

All clients MUST use the PKCE S256 code challenge method as described in Proof Key for Code Exchange by OAuth Public Clients and include the "code_challenge" parameter and "code_challenge_method", set to "S256", in the authorization request. Clients making a request to the authorization endpoint MUST use an unpredictable value for the state parameter with at least 128 bits of entropy. Clients MUST validate the value of the state parameter upon return to the redirect URI and MUST ensure that the state value is securely tied to the user's current session (e.g., by relating the state value to a session identifier issued by the client software to the browser). Clients that have multiple client types MUST have a separate client ID for each client type. Clients MUST include their full redirect URI in the authorization request. The client MAY specify a strength of authentication and maximum age to the authorization server that should be met when issuing an access token for the requesting client by including parameters in the authorization request: a space-separated string listing the authentication context class reference values in order of preference. The protected resource requires one of these values for the authentication event associated with the access token. As defined in Section 1.2 of OpenID Connect Core 1.0 , the authentication context conveys information about how authentication takes place (e.g., what authentication method(s) or assurance level to meet). It is out of scope of this document to determine how an organization semantically maps their digital identity practices to acr values that identify levels of assurance. a non-negative integer value that indicates the allowable elapsed time in seconds since the last active authentication event associated with the access token. Furthermore, if the authorization request is a follow-up to a prior request that did not meet the resource server's initial or subsequent authentication strength or recency requirements, the client should include the acr_values and/or max_age values sent by the resource server with the insuffient_user_authentication error code that specify expected strength and recency requirements to be provided to the authentication provider, such as the OpenID Provider, in a new authentication request. The following is a sample response from a client to the end user's browser for the purpose of redirecting the end user to the authorization server's authorization endpoint:

This causes the browser to send the following (non-normative) request to the authorization endpoint (inline wraps for display purposes only):

Clients MUST authenticate to the authorization server's token endpoint using either the private_key_jwt method as defined in OpenID Connect Core or the mutually-authenticated transport layer security (mTLS) request method defined in OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens. If using the private_key_jwt method, the request MUST be a JWT assertion as defined by the JWT Profile for OAuth 2.0 Client Authentication and Authorization Grants. The JWT assertion MUST be signed by the client using the client's private key. If using mTLS, the request MUST be made over a mutually authenticated TLS channel.

Confidential clients MUST have a public/private key pair for use in authentication to the token endpoint. These clients MUST either send the public key directly in the jwks field or register a jwks_uri that is reachable by the authorization server. It is RECOMMENDED that clients use a jwks_uri if possible as this allows for key rotation more easily. This applies to both dynamic and out-of-band client registration. The jwks field or the content available from the jwks_uri of a client MUST contain a public key in JSON Web Key Set (JWK Set) format. The authorization server MUST validate the content of the client's registered jwks_uri document and verify that it contains a JWK Set. The following example is of a 2048-bit RSA key:

For reference, the corresponding public/private key pair for this public key is the following (in JWK format):

Note that the second example contains both the public and private keys, while the first example contains the public key only.

Clients MUST use the authorization request header field mechanism to send bearer tokens as defined by . An example of an OAuth-protected call to the OpenID Connect UserInfo endpoint, sending the token in the Authorization header, follows:

All servers MUST conform to applicable recommendations found in the Security Considerations sections of and those found in the OAuth Threat Model Document. The authorization server MUST protect all communications to and from its OAuth endpoints using TLS as described in Section 1.4.

Authorization servers MUST support the authorization_code grant type and MAY support the client_credentials grant type. The implicit grant type MUST NOT be used. Authorization servers MUST limit each registered client (identified by a client ID) to a single client type only, since a single piece of software will be functioning at runtime as only one client type.

Authorization servers MUST enforce client authentication for confidential clients. Public clients cannot authenticate to the authorization server. Authorization servers MUST support the RS256 signature method (the Rivest, Shamir, and Adleman (RSA) signature algorithm with a 256-bit hash) and MAY use other asymmetric signature methods listed in JSON Web Algorithms (JWA) [RFC7518]. The authorization server MUST validate all redirect URIs for authorization code grant types. The authorization server MUST confirm thumbprints of client keys. Authorization servers MUST only grant access to higher level scope resources to clients that have permission to request these scope levels. Authorization servers MUST reject client authorization requests containing scopes that are outside their permission. Authorization servers MAY set the expiry time (exp) of access_tokens associated with higher level resources to be shorter than access_tokens for less sensitive resources. Authorization servers MAY allow a refresh_token issued at a higher level to be used to obtain an access_token for a lower level resource scope with an extended expiry time. The client MUST request both the higher level scope and lower level scope in the original authorization request. This allows clients to continue accessing lower level resources after the higher level resource access has expired -- without requiring an additional user authentication/authorization. When a client requests both a higher level scope and a lower level scope in the original authorization request, Authorization servers MAY allow refresh tokens issued at the higher level to be used to obtain an access_token for a lower level resource scope with an extended expiry time. This allows clients to continue accessing lower level resources after the higher level resource access has expired without requiring an additional user authentication/authorization.

Dynamic Registration allows for authorized Clients to on-board programmatically without administrative intervention. This is particularly important in ecosystems with many potential Clients, including Mobile Apps acting as independent Clients. Authorization servers MUST support dynamic client registration, and clients MAY register using the Dynamic Client Registration Protocol for authorization code grant types. Clients MUST NOT dynamically register for the client credentials grant type. Authorization servers MAY limit the scopes available to dynamically registered clients. Authorization servers MAY protect their Dynamic Registration endpoints by requiring clients to present credentials that the authorization server would recognize as authorized participants. Authorization servers MAY accept signed software statements as described in issued to client software developers from a trusted registration entity. The software statement can be used to tie together many instances of the same client software that will be run, dynamically registered, and authorized separately at runtime. The software statement MUST include the following client metadata parameters: array of redirect URIs used by the client; subject to the requirements listed in grant type used by the client; must be "authorization_code" or "client_credentials" human-readable name of the client URL of a web page containing further information about the client REQUIRED. Boolean value indicating server support for mutual-TLS client certificate-bound access tokens. OPTIONAL. Indicates the client will include the acr_values and max_age parameters in authorization requests, and send insufficient_user_authentication error messages in conformance with OAuth 2.0 Step Up Authentication Challenge Protocol. REQUIRED. A JSON array containing a list of the JWS alg values supported by the client for DPoP proof JWTs. client's public key in a JWK Set [RFC7517], or if jwks_uri is used it MUST be reachable by the Authorization Server and point to the client's public key set. If the PKI/tls_client_auth method is used, the public key must be issued by a trusted Certificate Authority. If either the self-signed mTLS method or private_key_jwt method for client authentication is used, the jwks MUST include a certificate. A client using the tls_client_auth authentication method MUST use exactly one of the below metadata parameters to indicate the certificate subject value that the authorization server is to expect when authenticating the respective client: String value specifying the expected subject DN of the client certificate. String value specifying the expected dNSName SAN entry in the client certificate. String value specifying the expected uniformResourceIdentifier SAN entry in the client certificate. It is NOT RECOMMENDED that authorization servers use IP address or email address to identify authenticating clients. It is also NOT RECOMMENDED that authorization servers use tls_client_auth_san_ip or tls_client_auth_san_email metadata values

When prompting the end user with an interactive approval page, the authorization server MUST indicate to the user: Whether the client was dynamically registered, or else statically registered by a trusted administrator. Whether the client is associated with a software statement, and in which case provide information about the trusted issuer of the software statement. What kind of access the client is requesting, including scope, protected resources (if applicable beyond scopes), and access duration. For example, if the user believes they are authorizing a very limited type of access, providing the access level at the consent screen may help the user make informed decisions about sharing sensitive information.

The authorization server MUST support and verify sender-constrained tokens. The Authorization Server MUST NOT issue the client an access token if the client included the tls_client_certificate_bound_access_tokens parameter in its registration metadata and makes a request to the token endpoint over connection not secured by TLS.

The authorization server MUST provide an OpenID Connect service discovery endpoint listing the components relevant to the OAuth 2.0 protocol: REQUIRED. The fully qualified issuer URL of the server REQUIRED. The fully qualified URL of the server's authorization endpoint defined by OAuth 2.0 REQUIRED. The fully qualified URL of the server's token endpoint defined by OAuth 2.0 REQUIRED. String of values corresponding to permitted methods for client authentication to the authorization server as defined in OAuth 2.0 Dynamic Client Registration Protocol. Within this profile, the server MUST provide one or more of the following values: "private_key_jwt", "tls_client_auth", and "self_signed_tls_auth". OPTIONAL. The fully qualified URL of the server's introspection endpoint defined by OAuth Token Introspection OPTIONAL. The fully qualified URL of the server's revocation endpoint defined by OAuth 2.0 Token Revocation OPTIONAL. A JSON object containing alternative authorization server endpoints that, when present, an OAuth client intending to perform mutual TLS uses in preference to the conventional endpoints. Use of this parameter enables isolation of mTLS behavior to only clients intending to use mTLS for authentication or sender-constraining tokens. Usage of the parameter is specified in OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens REQUIRED. The fully qualified URI of the server's JWK as defined in OAuth 2.0 Authorization Server Metadata. If the self_signed_tls_auth method is used, a jwks_uri MUST be registered and MUST include a certificate. If a client uses OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access TokensS for client authentication, exactly one authentication method metadata value MUST be included. Indicates that client authentication to the authorization server will occur with mutual TLS utilizing the PKI method of associating a certificate to a client. Indicates that client authentication to the authorization server will occur using mutual TLS with the client utilizing a self-signed certificate. If the authorization server is also an OpenID Connect Provider, it MUST provide a discovery endpoint meeting the requirements listed in Section 3.6 of OpenID Connect Core 1.0. The following example shows a JSON document found at the discovery endpoint for an authorization server:

It is RECOMMENDED that authorization servers provide cache information through HTTP headers and make the cache valid for at least one week. This allows clients and protected resources to cache the discovery information. Authorization servers MUST support the RS256 signature method (the Rivest, Shamir, and Adleman (RSA) signature algorithm with a 256-bit hash) and MAY use other asymmetric signature methods listed in the JSON Web Algorithms (JWA [RFC7518]) ) specification. The authorization server MUST provide its public key in JWK Set format. The key MUST contain the following fields: The key ID of the key pair used to sign this token The key type The default algorithm used for this key The following is an example of a 2048-bit RSA public key:

Token revocation allows a client to signal to an authorization server that a given token will no longer be used. Authorization servers MUST provide a revocation endpoint URL as specified in OAuth 2.0 Token Revocation for end users to view a list of clients that have been granted access to resources on the user's behalf and for end users to revoke this access. Authorization servers MUST revoke a token if the client requesting the revocation is the client to which the token was issued, the client has permission to revoke tokens, and the token is able to be revoked. Authorizatin servers MUST NOT allow a client to use a token after it is revoked.

Authorization servers MUST require use of PKCE (Proof Key for Code Exchange by OAuth Public Clients) by all clients and reject requests to the authorization endpoint from clients that do not contain a code challenge. Authorization servers MUST support the S256 code challenge method. Authorization servers MUST NOT allow a client to use the plain code challenge method. The PKCE code_verifier value MUST contain at least 128 bits of entropy. Authorization servers MUST confirm thumbprints of client keys.

The authorization server MUST validate all redirect URIs for authorization code grant types. To prevent open redirection and other injection attacks, the authorization server MUST match the entire redirect URI using an exact string match against registered values and MUST reject requests with an invalid or missing redirect URI.

Authorization servers MAY issue refresh tokens to clients.

Authorization servers respond to an Authorization Request from a client with an Authorization Response. The following fields MUST be included in the response: REQUIRED. The value of the state parameter passed in in the authentication request. This value MUST match exactly. REQUIRED. The authorization code, a random string issued by the IdP to be used in the request to the token endpoint. PKCE parameters MUST be associated with the authorization code as per Section 4.4 of Proof Key for Code Exchange by OAuth Public Clients (PKCE). The following is an example response:

Authorization servers MUST issue cryptographically signed sender-constrained tokens in the JSON Web Token (JWT) format as defined in JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens. The information carried in the JWT is intended to allow a protected resource to quickly test the integrity of the token without additional network calls, and to allow the protected resource to determine which authorization server issued the token. The protected resource MAY use the authorization server token introspection service to retrieve additional security information about the token. The server MUST issue tokens as JWTs with, at minimum, the following claims: The issuer URL of the server that issued the token The client id of the client to whom this token was issued The expiration time (integer number of seconds since from 1970-01-01T00:00:00Z UTC), after which the token MUST be considered invalid A unique JWT Token ID value with at least 128 bits of entropy. This value MUST NOT be re-used in another token. Clients MUST check for reuse of jti values and reject all tokens issued with duplicate jti values. The identifier of the end-user that authorized this client, or the client id of a client acting on its own behalf (such as a bulk transfer). Since this information could potentially leak private user information, it should be used only when needed. End-user identifiers SHOULD be pairwise anonymous identifiers unless the audience requires otherwise. The audience of the token, an array containing the identifier(s) of protected resource(s) for which the token is valid, if this information is known. The aud claim may contain multiple values if the token is valid for multiple protected resources. Note that at runtime, the authorization server may not know the identifiers of all possible protected resources at which a token may be used. The value of the scope claim is a JSON string containing a space-separated list of scopes associated with the token, in the format described in Section 3.3 of The OAuth 2.0 Authorization Framework. The "iat" (issued at) claim identifies the time at which the JWT was issued. This claim can be used to determine the age of the JWT. Its value MUST be a number containing a NumericDate value. The confirmation claim, as defined in Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs) and OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens is used in a JWT to contain members used to identify the proof-of-possession key. When OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokensis used, the confirmation claim value MUST be computed using the X.509 Certificate SHA-256 Thumbprint and include confirmation method value "x5t#256". When OAuth 2.0 Demonstrating Proof of Possession (DPoP) is used, the confirmation claim value MUST be computed using the JWK SHA-256 Thumbprint of the DPoP public key and include conformation method value jkt. In order to support backwards compatibility, AS MAY include the azp claim while resource servers modernize. The following sample claim set illustrates the use of the required claims for an access token as defined in this profile; additional claims MAY be included in the claim set:

The access tokens MUST be signed with JWS . If private_key_jwt is used, the authorization server MUST support the RS256 signature method for tokens and MAY use other asymmetric signing methods as defined in the IANA JSON Web Signatures and Encryption Algorithms registry . The JWS header MUST contain the following fields: The key ID of the key pair used to sign this token This example access token has been signed with the server's private key using RS256:

Refresh tokens SHOULD be signed with JWS using the same private key and contain the same set of claims as the access tokens. The authorization server MAY encrypt access tokens and refresh tokens using JWE . Encrypted access tokens MUST be encrypted using the public key of the protected resource. Encrypted refresh tokens MUST be encrypted using the authorization server's public key. The client SHOULD use a certificate to sender-constrain tokens that is distinct from the certificate used to connect to the protected resource.

Access tokens SHOULD have a valid lifetime no greater than one hour, and refresh tokens (if issued) SHOULD have a valid lifetime no greater than twenty-four hours. Specific applications MAY issue tokens with different lifetimes. Any active token MAY be revoked at any time.

Scopes define individual pieces of authority that can be requested by clients, granted by resource owners, and enforced by protected resources. Specific scope values will be highly dependent on the specific types of resources being protected in a given interface. OpenID Connect, for example, defines scope values to enable access to different attributes of user profiles. Authorization servers SHOULD define and document default scope values that will be used if an authorization request does not specify a requested set of scopes. To facilitate general use across a wide variety of protected resources, authorization servers SHOULD allow for the use of arbitrary scope values at runtime, such as allowing clients or protected resources to use arbitrary scope strings upon registration. Authorization servers MAY restrict certain scopes from use by dynamically registered systems or public clients. Refer to for further information about displaying scopes to end users.

Token introspection allows a protected resource to query the authorization server for metadata about a token. Authorization servers MUST NOT allow clients to use token introspection endpoints. The protected resource makes a request over a mutually authenticated TLS connection like the following to the token introspection endpoint:

The client assertion parameter is structured as described in . Authorization servers respond to an introspection request with a JSON object containing the following fields as defined in OAuth 2.0 Token Introspection. Boolean value indicating whether or not this token is currently active at this authorization server. Tokens that have been revoked, have expired, or were not issued by this authorization server are considered non-active. Space-separated list of OAuth 2.0 scope values represented as a single string. Timestamp of when this token expires (integer number of seconds since from 1970-01-01T00:00:00Z UTC) An opaque string that uniquely identifies the user who authorized this token at this authorization server (if applicable). This string MAY be diversified per client. An opaque string that uniquely identifies the OAuth 2.0 client that requested this token The following example is a response from the introspection endpoint:

Authorization servers MUST require authentication of resource servers for the introspection endpoint using either private_key_jwt or Mutual-TLS methods as described for clients in . Authorization servers MUST NOT allow clients to use token introspection endpoints.

Protected resources MUST interpret access tokens using either JWT, token introspection, or a combination of the two Protected resources MUST check the aud (audience) claim in tokens to ensure that it includes the protected resource's identifier. Protected resources MUST accept tokens passed in the authorization header as described in . A protected resource MUST NOT accept tokens passed in the form parameter or query parameter methods. Protected resources MUST define and document which scopes are required for access to the resource and any authentication strength or recency requirements for each scope. If a client mTLS to sender-constrain tokens, the protected resource MUST verify that the certificate matches the certificate associated with the access token. If they do not match, the resource access attempt MUST be denied. Protected resources MAY use authentication context or step up authentication to implement access controls. If the authentication event associated with the access token does not satisfy the requirements of the resource server for the given request, the protected resource MUST return a 401 Unauthorized status code along with a WWW-Authenticate header as defined in OAuth 2.0 Step Up Authentication Challenge Protocol. This header MUST include the insufficient_user_authentication error code to indicate that the presented access token is inadequate. Additionally, the response MUST include the acr_values and/or max_age auth-params to communicate the necessary authentication context class reference values and the allowable elapsed time since the last active authentication event, respectively. The acr_values parameter should list the required authentication context class reference values in order of preference, while the max_age parameter should indicate the maximum permissible time in seconds since the last user authentication. The mechanisms by which the protected resource determines whether the authentication requirements are met are outside the scope of this profile. Furthermore, protected resources MAY include both acr_values and max_age if both are relevant. Protected resources MAY include the scope parameter if additional scopes are required to access the resource, as per Section 3.1 of The OAuth 2.0 Authorization Framework: Bearer Token Usage.

Protected Resources grant access to clients if they present a valid sender-constrained access_token with the appropriate scopes. Resource servers trust the authorization server to authenticate the end user and client appropriately for the importance, risk, and value level of the protected resource scope. Protected resources MAY use OAuth 2.0 Step Up Authentication Challenge Protocol to implement access controls. If a protected resources requires a higher end-user authentication trust level to access certain resources, the protected resource MUST associate those resources with a unique scope and MUST associate acceptable acr values for each scope as descibed in OAuth 2.0 Step Up Authentication Challenge Protocol. Protected Resources may also specify a max_age for each scope. Protected resources MAY include the scope parameter if additional scopes are required to access the resource, as per Section 3.1 of The OAuth 2.0 Authorization Framework: Bearer Token Usage.

For example, a resource server associates scopes with data classified as "public" and "sensitive". Access to data with scope "sensitive" requires the user to perform a two-factor authentication and limits those access grants to only 15 minutes. The resource server associates scope "sensitive" with acr="MFA". For a client to obtain access to both "public" and "sensitive" data, it makes an authorization request to the authorization server with scope=public+sensitive, acr_values="MFA", and max_age=900. The authorization server authenticates the end-user as required to meet the required trust level (two-factor authentication or some approved equivalent) and issues an access_token for the "public" and "sensitive" scopes with an expiry time of 15 minutes and a refresh_token for the "public" scope with an expiry time of 24 hrs. The client can access both "public" and "sensitive" data for 15mins with the access_token. When the access_token expires, the client will NOT be able to access "public" or "sensitive" data any longer as the access_token has expired, and must obtain a new access_token. The client makes a refresh token request (as described in OAuth 2.0 section 6) with the refresh_token, and the reduced scope of just "public". The token endpoint validates the refresh_token, and issues a new access_token for just the "public" scope with an expiry time set to 24hrs. An access grant request for a new access_token with the "sensitive" scope would be rejected, and require the client to get the end-user to re-authenticate/authorize the "sensitive" scope request. In this manner, protected resources and authorization servers work together to meet risk tolerance levels for sensitive resources and end-user authentication.

Protected resources MUST provide a JWKS URI endpoint to distribute public keys to support signing, encryption, and authentication to authorization server revocation and introspection endpoints. OAuth 2.0 Protected Resource Metadata defines a metadata format that a client or authorization server can use to obtain the information needed to interact with a protected resource. This metadata facilitates enhanced interoperability and security, including advertisement and discovery of a protected resource's public key via its jwks_uri. Protected resources calling the introspection endpoint MUST use credentials distinct from any other OAuth client registered at the authorization server. Protected resources MAY cache the response from the introspection endpoint for a period of time no greater than half the lifetime of the token. A protected resource MUST NOT accept a token that is not active according to the response from the introspection endpoint. Protected resources MUST ensure that the rights associated with the token are sufficient to grant access to the resource. For example, this can be accomplished by querying the scopes and acr value associated with the token from the authorization server's token introspection endpoint. Protected resources MUST limit which authorization servers it will accept valid tokens from. A resource server MAY accomplish this using a whitelist of trusted servers, a dynamic policy engine, or other means.

For a comprehensive protection against network attackers, all endpoints should additionally use DNSSEC to protect against DNS spoofing attacks that can lead to the issuance of rogue domain-validated TLS certificates.

Authorization server, client, and protected resource implementations SHOULD consider including requirements from Best Current Practice for OAuth 2.0 Security, JSON Web Token Best Current Practices and JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens that are not explicitly mentioned in this profile.

Authorization Servers SHOULD take device posture into account, when possible. Some examples of device posture include: the user's lock screen setting the client's level of privilege over the device operating system (e.g. if the client has 'root access', the device operating system may be compromised to gain additional privileges not intended by the vendor) the availability of a device attestation to validate the client Specific policies or capabilities are outside the scope of this specification. This profile does not protect against the attacks described in The Stronger Attacker Model, in which an attacker could inject the authorization request and read the authorization response. Although using request object signatures would provide mitigation, this profile does not require request object signatures because of the lack of available implementations.

This profile addresses the privacy threats identified in Privacy Considerations for Internet Protocols with normative language throughout the document. In particular, this profile requires the use of TLS for all network connections, PKCE, and sender constrained tokens to mitigate the threats in In OpenID Connect implementations, cilents and servers SHOULD implement the privacy threat mitigations in Section 17 of OpenID Connect Core 1.0.

Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are widely used to protect data exchanged over application protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the last few years, several serious attacks on TLS have emerged, including attacks on its most commonly used cipher suites and their modes of operation. This document provides recommendations for improving the security of deployed services that use TLS and DTLS. The recommendations are applicable to the majority of use cases. This document describes best current security practice for OAuth 2.0. It updates and extends the threat model and security advice given in RFCs 6749, 6750, and 6819 to incorporate practical experiences gathered since OAuth 2.0 was published and covers new threats relevant due to the broader application of OAuth 2.0. Further, it deprecates some modes of operation that are deemed less secure or even insecure. Nomura Research Institute, Ltd. Ping Identity Microsoft Google Salesforce Nomura Research Institute, Ltd. Ping Identity Microsoft IllumilaJSON

The OpenID Community would like to thank the following people for their contributions to this specification: Mark Russel, Mary Pulvermacher, David Hill, Dale Moberg, Adrian Gropper, Eve Maler, Danny van Leeuwen, John Moehrke, Aaron Seib, John Bradley, Debbie Bucci, Josh Mandel, Sarah Cecchetti, Giuseppe De Marco, Joseph Heenan, Jim Fenton, Ryan Galluzzo, Bjorn Hjelm, Aaron Parecki, Michael B. Jones, and Stas Mironov. Special thank you to the original iGov Profile editors: Paul Grassi, Justin Richer, and Michael Varley. The original version of this specification was part of the Secure RESTful Interfaces project from The MITRE Corporation, available online at http://secure-restful-interface-profile.github.io/pages/

Copyright (c) 2025 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, Final Specification, or Final Specification Incorporating Errata Corrections solely for the purposes of (i) developing specifications, and (ii) implementing Implementers Drafts, Final Specifications, and Final Specification Incorporating Errata Corrections 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 (found at openid.net) requires contributors to offer a patent promise not to assert certain patent claims against other contributors and against implementers. OpenID 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.

[[ To be removed from the final specification ]] -08 Added description of resource server requirements for authentication context and step-up Restructured the document so the text flows better Added a method to securely discover or declare JWKS-URI for PR/RS Removed public clients to align with FAPI Moved requirements to correct section Realigned requirements among AS, client, and PR/RS Changed date, version, and document history -06-07 Addressed comments from WGLC request Jan 31, 2025 -05 Updated BCP mitigations, aligned with FAPI Harmonized cryptography, sender constrained tokens with FAPI Added requirement and optionality for authentication context and support for Step-up (RFC 9470) Added Privacy Considerations (RFC 6973) Added optionality to support enterprise tailoring, especially RFC 8705 mTLS with PKI -04 Enable building with https://author-tools.ietf.org/. Applied OpenID specification conventions. -03 First Implementer's Draft -2017-06-01 Aligned with prior version of iGov. Added guidance text around using scopes and refresh_tokens to protect sensitive resources. Removed ACR reference. -2018-05-07 Imported content from HEART OAuth profile.