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OpenID Heart 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 to (but not limited to) the healthcare domain.

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. To achieve this flexibility, the standard makes many security controls optional. OAuth implementations using only the minimum mandatory security measures require minimal effort on the part of developers and users, but they also fail to prevent known attacks and are unsuitable for protecting sensitive data. The OAuth 2.0 client and server profiles defined in this document serve two purposes: 1. Define a mandatory baseline set of security controls suitable for a wide range of use cases, while maintaining reasonable ease of implementation and functionality 2. Identify optional advanced security controls for sensitive use cases where heightened risks justify more stringent controls that increase the required implementation effort and may reduce or restrict functionality This OAuth profile is intended to be shared broadly, and ideally to influence OAuth implementations in other domains besides health care.

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.

The following profile descriptions give patterns of deployment for use in different types of client applications based on the OAuth grant type. The resource owner password credentials grant type defined in is intentionally omitted from this discussion, and MUST NOT be used under these profiles. Additional grant types, such as assertions, chained tokens, or other mechanisms, are out of scope of this profile and must be covered separately by appropriate profile documents.

This client type applies to clients that act on behalf of a particular resource owner and require delegation of that user’s authority to access the protected resource. Furthermore, these clients are capable of interacting with a separate web browser application to facilitate the resource owner’s interaction with the authentication endpoint of the authorization server. These clients MUST use the authorization code flow of OAuth 2 by sending the resource owner to the authorization endpoint to obtain authorization. The user MUST authenticate to the authorization endpoint. The user’s web browser is then redirected back to a URI hosted by the client, from which the client can obtain an authorization code passed as a query parameter. The client then presents that authorization code along with its own credentials to the authorization server's token endpoint to obtain an access token. The authorization code flow is supported only for confidential clients. Examples of this client type include web applications and native applications that can store installation-instance-specific client credentials securely. For applications that can have multiple identical instances operating in different environments and running simultaneously, such as with a native application on a mobile device, it is RECOMMENDED to generate a unique key on the device and use dynamic client registration to register that key with the authorization server. Client credentials MUST NOT be shared among instances of client software. This client type MAY request and be issued a refresh token if the security parameters of the access request allow for it.

This client type applies to clients that act on behalf of a particular resource owner and require delegation of that user’s authority to access the protected resource. Furthermore, these clients are embedded within a web browser and effectively share an active session between systems. These clients use the implicit flow of OAuth 2 by sending a resource owner to the authorization endpoint to obtain authorization. The user MUST authenticate to the authorization endpoint. The user’s web browser is then redirected back to a URI hosted by the client, from which the client can directly obtain an access token. Since the client itself never authenticates to the server and the token is made available directly to the browser, this flow is appropriate only for clients embedded within a web browser, such as a JavaScript client with no back-end server component. Wherever possible, it is preferable to use the authorization code flow due to its superior security properties. This client type MUST NOT request or be issued a refresh token. Access tokens issued to this type of client MUST be short lived and SHOULD expire when the user's authenticated session with the client expires.

This profile applies to clients that connect directly to protected resources and do not act on behalf of a particular resource owner, such as those clients that facilitate bulk transfers. These clients use the client credentials flow of OAuth 2 by sending a request to the token endpoint with the client's credentials and obtaining an access token in the response. Since this profile does not involve an authenticated user, this flow is appropriate only for trusted applications, such as those that would traditionally use a developer key. For example, a partner system that performs bulk data transfers between two systems would be considered a direct access client. This client type MUST NOT request or be issued a refresh token.

Full clients and direct access clients as defined above MUST authenticate to the authorization server's token endpoint using a JWT assertion as defined by the JWT Profile for OAuth 2.0 Client Authentication and Authorization Grants and the private_key_jwt method defined in OpenID Connect Core. The assertion MUST use the claims as follows: the client ID of the client creating the token the client ID of the client creating the token the URL of the authorization server's token endpoint the time that the token was created by the client the expiration time, after which the token MUST be considered invalid a unique identifier generated by the client for this authentication. This identifier MUST contain at least 128 bits of entropy and MUST NOT be re-used by any subsequent authentication token. The following sample claim set illustrates the use of the required claims for a client authentication JWT as defined in this profile; additional claims MAY be included in the claim set.

The JWT assertion MUST be signed by the client using the client's private key. See for mechanisms by which the client can make its public key known to the server. The authorization server 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) specification. The following sample JWT contains the above claims and has been signed using the RS256 JWS algorithm and the client's own private key (with line breaks for display purposes only):

This is sent in the request to the token endpoint as in the following example:

Authorization servers MAY require some clients to additionally authenticate using mutual Transport Layer Security (TLS) authentication, with the client's TLS certificate having been registered at the authorization server alongside its key. Due to problems inherent in configuring a large mutual TLS network at scale, it is RECOMMENDED by this profile that such authentication be limited to instances where the security benefits sufficiently outweigh the complications.

Full clients and browser-embedded 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 MUST include their full redirect URIs in the authorization request. To prevent open redirection and other injection attacks, the authorization server MUST match the entire redirect URI using a direct string comparison against registered values and MUST reject requests with invalid or missing redirect URIs. The following is a sample response from a web-based 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 request to the authorization endpoint:

All clients MUST register with the authorization server. For client software that may be installed on multiple client instances, such as native applications or web application software, each client instance MUST receive a unique client identifier from the authorization server. Clients using the authorization code or client credentials grant type MUST have a public and private key pair for use in authentication to the token endpoint. These clients MUST register their public keys in their client registration metadata by either sending the public key directly in the jwks field or by registering a jwks_uri that MUST be reachable by the authorization server. It is RECOMMENDED that clients use a jwks_uri if possible as this allows for key rotation more easily. 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 using the authorization code or implicit grant types MUST register their full redirect URIs. The Authorization Server MUST validate the redirect URI given by the client at the authorization endpoint using strict string comparison. A client 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 the local domain of the client (e.g., http://localhost/) Hosted on a client-specific non-remote-protocol URI scheme (e.g., myapp://) Clients MUST NOT have URIs in more than one category and SHOULD NOT have multiple redirect URIs on different domains. 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”).

Authorization servers MUST support dynamic client registration, and clients MAY register using the Dynamic Client Registration Protocol for authorization code or implicit 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 MUST signal to end users that a client was dynamically registered on the authorization screen. Authorization servers MAY accept signed software statements as described in issued to client software developers from a trusted registration entity, and MUST indicate to the end user that such a statement was used in the client's registration. 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 "implicit” client's public key in JWK Set format; if jwks_uri is used it MUST be reachable by the Authorization Server and point to the client's public key set human-readable name of the client URL of a web page containing further information about the client

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 support the authorization_code, implicit, and client_credentials grant types as described above. The authorization server MUST limit each registered client (identified by a client ID) to a single grant type only. The authorization server MUST enforce client authentication as described above for the authorization code and client credentials grant types. The authorization server MUST validate all redirect URIs for authorization code and implicit grant types. The authorization server MUST protect all communications to and from its OAuth endpoints using TLS.

The authorization server MUST provide an OpenID Connect service discovery endpoint listing the components relevant to the OAuth protocol: The fully qualified issuer URL of the server The fully qualified URL of the server's authorization endpoint defined by OAuth 2.0 The fully qualified URL of the server's token endpoint defined by OAuth 2.0 The fully qualified URL of the server's introspection endpoint defined by OAuth Token Introspection The fully qualified URL of the server's revocation endpoint defined by OAuth 2.0 Token Revocation The fully qualified URI of the server's public key in JWK Set format If the authorization server is also an OpenID Connect Provider, it MUST provide a discovery endpoint meeting the requirements listed in Section 6 of the HEART OpenID Connect profile. The following example shows the JSON document found at a discovery endpoint for an authorization server:

Clients and protected resources SHOULD cache this discovery information. It is RECOMMENDED that servers provide cache information through HTTP headers and make the cache valid for at least one week. The server MUST provide its public key in JWK Set format, such as the following 2048-bit RSA public key:

Clients and protected resources SHOULD cache this key. It is RECOMMENDED that servers provide cache information through HTTP headers and make the cache valid for at least one week.

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 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) the key ID of the keypair used to sign this token 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 server MAY issue tokens with an aud (audience) claim whose value is 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. 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. The authorization server MUST support the RS256 signature method for tokens and MAY use other asymmetric signing methods. 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 public key and contain the same set of claims as the access tokens. The authorization server MAY encrypt access tokens and refresh tokens using JWE. Access tokens MUST be encrypted using the public key of either the protected resource or the authorization server itself. Refresh tokens MUST be encrypted using the authorization server's public key.

This profile provides RECOMMENDED lifetimes for different types of tokens issued to different types of clients. Specific applications MAY issue tokens with different lifetimes. Any active token MAY be revoked at any time. For clients using the authorization code grant type, 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. For clients using the implicit grant type, access tokens SHOULD have a valid lifetime no greater than fifteen minutes. For clients using the client credentials grant type, access tokens SHOULD have a valid lifetime no greater than six hours.

The authorization server MUST supply token revocation and token introspection endpoints to allow clients and protected resources to manage the lifecycle of issued tokens. Token revocation allows a client to signal to an authorization server that a given token will no longer be used. A client MUST immediately discard the token and not use it again after revoking it. Token introspection allows a protected resource to query the authorization server for metadata about a token. The protected resource makes a request like the following to the token introspection endpoint:

The client assertion parameter is structured as described in . The server responds to an introspection request with a JSON object representing the token containing the following fields as defined in the token introspection specification: 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) 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:

The authorization server MUST require authentication for both the revocation and introspection endpoints as described in . Protected resources calling the introspection endpoint MUST use credentials distinct from any other OAuth client registered at the server. A protected resource 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.

The protected resource MUST support bearer tokens passed in the Authentication header as defined by . Protected resources MAY support the form-parameter or query-parameter methods in . Authorized requests MUST be made over TLS, and clients MUST validate the protected resource server's certificate. An example of an OAuth-protected call to the OpenID Connect UserInfo endpoint, sending the token in the Authorization header, follows:

The protected resource MUST check the audience claim, if it exists in the token, to ensure that it includes the protected resource's identifier. The protected resource 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 associated with the token from the authorization server's token introspection endpoint.

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. Protected resources MUST define and document which scopes are required for access to the resource. 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.

The preceding portions of this OAuth profile provide a level of security adequate for a wide range of use cases, while still maintaining relative ease of implementation and usability for developers, system administrators, and end users. The following are some additional security measures that can be employed for use cases where elevated risks justify the use of additional controls at the expense of implementation effort and usability. This section also addresses future security capabilities, currently in the early draft stages, being added to the OAuth standard suite.

The OAuth 2.0 specification requires the use of TLS to protect several different connections among the parties involved in an OAuth transaction, but in each case only server authentication is required. Clients could additionally be required to negotiate a mutually-authenticated TLS connection: When connecting to the Authorization server's Token Endpoint to retrieve access and refresh tokens When connecting to protected resources Stronger client authentication to the Token Endpoint reduces the risk of a captured Authorization Code being used to obtain tokens. Stronger client authentication to the protected resource, combined with validation that the authenticated client is identified in the azp token claim, reduces the risk of captured tokens being used by unauthorized clients. In both cases, mutual TLS authentication provides much stronger protection against man-in-the-middle attacks than server authentication alone. Apart from the difficulty of implementing Public Key Infrastructure (PKI) solutions in distributed, cross-organization settings, one concern with this approach is the clients’ highly variable capabilities to protect private keys. Web application clients may be able to provide strong protection, but with native clients such as mobile apps, the key may be stored in a hardware security module or in plaintext in flash storage.

OAuth proof of possession tokens are currently defined in a set of drafts under active development in the Internet Engineering Task Force (IETF) OAuth Working Group. While a bearer token can be used by anyone in possession of the token, a proof of possession 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; a variety of mechanisms for doing this are outlined in the draft OAuth 2.0 Proof-of-Possession (PoP) Security Architecture. When the client presents the token to the protected resource, it is also required to demonstrate possession of the corresponding key (e.g., by creating a cryptographic hash or signature of the request). Proof of Possession tokens are somewhat analogous to the Security Assertion Markup Language's (SAML's) Holder-of-Key mechanism for binding assertions to user identities. Proof of possession could prevent a number of attacks on OAuth that entail the interception of 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. Additionally, portions of the HTTP request could be protected by the same signature used in presentation of the token. Proof of possession tokens may not provide all of the same protections as PKI authentication, but they are far less challenging to implement on a distributed scale.

All transactions MUST be protected in transit by TLS as described in BCP195. All clients MUST conform to applicable recommendations found in the Security Considerations sections of and those found in the OAuth 2.0 Threat Model and Security Considerations document.

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. Nomura Research Institute, Ltd. Ping Identity Microsoft Google Salesforce Nomura Research Institute, Ltd. Ping Identity Microsoft Illumila

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, and Sarah Squire. 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) 2015 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.

-2016-02-15 Implementer's Draft 1 -2015-11-30 Clarified client instances. Replaced "mitre.org" with "example.com" (JWTs need to be regenerated). Fixed specification references to new RFCs. Clarified scope flexibility. Clarified dynamic registration requirement. Added some UX requirements and guidance. Added security considerations section and TLS BCP reference. -2015-04-24 Fixed references to make it compile -2015-04-01 Imported content from Secure RESTful OAuth profile.