International Government Assurance Profile (iGov) for OAuth 2.0

	iGov OAuth 2.0	August 2023
Richer, et al.	Standards Track	[Page]

Abstract

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.¶

2. Client Profiles

2.1. Client Types

The following profile descriptions give patterns of deployment for use in different types of client applications based on the OAuth grant type. 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.¶

2.1.1. Full Client with User Delegation

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 service, 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 (private_key_jwt) to the authorization server's token endpoint to obtain an access token.¶

These clients MUST be associated with a unique public key, as described in Section 2.2 .¶

This client type MAY request and be issued a refresh token if the security parameters of the access request allow for it.¶

2.1.2. Native Client with User Delegation

This client type applies to clients that act on behalf of a particular resource owner, such as an app on a mobile platform, 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. In particular, this client type runs natively on the resource owner's device, often leading to many identical instances of a piece of software operating in different environments and running simultaneously for different end users.¶

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 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 to the authorization server's token endpoint to obtain an access token.¶

Native clients MUST either:¶

use dynamic client registration to obtain a separate client id for each instance, or¶
act as a public client by using a common client id and use PKCE [RFC7636] to protect calls to the token endpoint.¶

Native applications using dynamic registration SHOULD generate a unique public and private key pair on the device and register that public key value with the authorization server. Alternatively, an authorization server MAY issue a public and private key pair to the client as part of the registration process. In such cases, the authorization server MUST discard its copy of the private key. Client credentials MUST NOT be shared among instances of client software.¶

Dynamically registered native applications MAY use PKCE.¶

Native applications not registering a separate public key for each instance are considered Public Clients, and MUST use PKCE [RFC7636] with the S256 code challenge mechanism. Public Clients do not authenticate with the Token Endpoint in any other way.¶

2.1.3. Direct Access Client

This client type MUST NOT request or be issued a refresh token.¶

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.¶

2.2. Client Registration

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 MAY receive a unique client identifier from the authorization server. Clients that share client identifiers are considered public clients.¶

Client registration MAY be completed by either static configuration (out-of-band, through an administrator, etc...) or dynamically.¶

2.2.1. Redirect URI

Clients using the authorization code grant type 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 a client-specific non-remote-protocol URI scheme (e.g., myapp://)¶
Hosted on the local domain of the client (e.g., http://localhost/)¶

Clients 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").¶

2.3. Connection to the Authorization Server

2.3.1. Requests to the Authorization Endpoint

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 URI 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 an invalid or missing redirect URI.¶

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:¶

HTTP/1.2 302 Found
Cache-Control: no-cache
Connection: close
Content-Type: text/plain; charset=UTF-8
Date: Wed, 07 Jan 2015 20:24:15 GMT
Location: https://idp-p.example.com/authorize?client_id=55f9f559-2496-49d4-b6c3-351a58
6b7484&nonce=cd567ed4d958042f721a7cdca557c30d&response_type=code&scope=openid+email&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
Status: 302 Found

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

GET /authorize?
   client_id=55f9f559-2496-49d4-b6c3-351a586b7484
  &nonce=cd567ed4d958042f721a7cdca557c30d
  &response_type=code
  &scope=openid+email
  &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb HTTP/1.1
Host: idp-p.example.com

2.3.2. Requests to the Token Endpoint

Full clients, native clients with dynamically registered keys, 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 [RFC7523] using only the private_key_jwt method defined in OpenID Connect Core [OpenID.Core] . The assertion MUST use the claims as follows:¶

iss: the client ID of the client creating the token¶
sub: the client ID of the client creating the token¶
aud: the URL of the authorization server's token endpoint¶
iat: the time that the token was created by the client¶
exp: the expiration time, after which the token MUST be considered invalid¶
jti: 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.¶

{
   "iss": "55f9f559-2496-49d4-b6c3-351a586b7484",
   "sub": "55f9f559-2496-49d4-b6c3-351a586b7484",
   "aud": "https://idp-p.example.com/token",
   "iat": 1418698788,
   "exp": 1418698848,
   "jti": "1418698788/107c4da5194df463e52b56865c5af34e5595"
}

The JWT assertion MUST be signed by the client using the client's private key. See Section 2.2 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 [RFC7518] ) 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):¶

eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.ew0KICAgImlzcyI6ICI1NWY5ZjU1OS0yNDk2LTQ5Z
DQtYjZjMy0zNTFhNTg2Yjc0ODQiLA0KICAgInN1YiI6ICI1NWY5ZjU1OS0yNDk2LTQ5ZDQtYjZjMy0
zNTFhNTg2Yjc0ODQiLA0KICAgImF1ZCI6ICJodHRwczovL2lkcC1wLmV4YW1wbGUuY29tL3Rva2VuI
iwNCiAgICJpYXQiOiAxNDE4Njk4Nzg4LA0KICAgImV4cCI6IDE0MTg2OTg4NDgsDQogICAianRpIjo
gIjE0MTg2OTg3ODgvMTA3YzRkYTUxOTRkZjQ2M2U1MmI1Njg2NWM1YWYzNGU1NTk1Ig0KfQ.t-_gX8
JQGq3G2OEc2kUCQ8zVj7pqff87Sua5nktLIHj28l5onO5VpsL4sRHIGOvrpo7XO6jgtPWy3iLXv3-N
Lyo1TWHbtErQEGpmf7nKiNxVCXlGYJXSDJB6shP3OfvdUc24urPJNUGBEDptIgT7-Lhf6BbwQNlMQu
bNeOPRFDqQoLWqe7UxuI06dKX3SEQRMqcxYSIAfP7CQZ4WLuKXb6oEbaqz6gL4l6p83G7wKGDeLETO
THszt-ZjKR38v4F_MnSrx8e0iIqgZwurW0RtetEWvynOCJXk-p166T7qZR45xuCxgOotXY6O3et4n7
7GtgspMgOEKj3b_WpCiuNEwQ

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

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded
User-Agent: Rack::OAuth2 (1.0.8.7) (2.5.3.2, ruby 2.1.3 (2014-09-19))
Accept: */*
Date: Tue, 16 Dec 2014 02:59:48 GMT
Content-Length: 884
Host: idp-p.example.com

grant_type=authorization_code
&code=sedaFh
&scope=openid+email
&client_id=55f9f559-2496-49d4-b6c3-351a586b7484
&redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
&client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.ew0KICAgImlzcyI6ICI1NWY
5ZjU1OS0yNDk2LTQ5ZDQtYjZjMy0zNTFhNTg2Yjc0ODQiLA0KICAgInN1YiI6ICI1NWY5ZjU1OS0yN
Dk2LTQ5ZDQtYjZjMy0zNTFhNTg2Yjc0ODQiLA0KICAgImF1ZCI6ICJodHRwczovL2lkcC1wLmV4YW1
wbGUuY29tL3Rva2VuIiwNCiAgICJpYXQiOiAxNDE4Njk4Nzg4LA0KICAgImV4cCI6IDE0MTg2OTg4N
DgsDQogICAianRpIjogIjE0MTg2OTg3ODgvMTA3YzRkYTUxOTRkZjQ2M2U1MmI1Njg2NWM1YWYzNGU
1NTk1Ig0KfQ.t-_gX8JQGq3G2OEc2kUCQ8zVj7pqff87Sua5nktLIHj28l5onO5VpsL4sRHIGOvrpo
7XO6jgtPWy3iLXv3-NLyo1TWHbtErQEGpmf7nKiNxVCXlGYJXSDJB6shP3OfvdUc24urPJNUGBEDpt
IgT7-Lhf6BbwQNlMQubNeOPRFDqQoLWqe7UxuI06dKX3SEQRMqcxYSIAfP7CQZ4WLuKXb6oEbaqz6g
L4l6p83G7wKGDeLETOTHszt-ZjKR38v4F_MnSrx8e0iIqgZwurW0RtetEWvynOCJXk-p166T7qZR45
xuCxgOotXY6O3et4n77GtgspMgOEKj3b_WpCiuNEwQ

2.3.3. Client Keys

Clients using the authorization code grant type or direct access clients using the 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. This applies to both dynamic and static (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) [RFC7517] 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:¶

{
   "keys": [
     {
       "alg": "RS256",
       "e": "AQAB",
       "n": "kAMYD62n_f2rUcR4awJX4uccDt0zcXRssq_mDch5-ifcShx9aTtTVza23P
Tn3KaKrsBXwWcfioXR6zQn5eYdZQVGNBfOR4rxF5i7t3hfb4WkS50EK1gBYk2lO9NSrQ-xG
9QsUsAnN6RHksXqsdOqv-nxjLexDfIJlgbcCN9h6TB-C66ZXv7PVhl19gIYVifSU7liHkLe
0l0fw7jUI6rHLHf4d96_neR1HrNIK_xssr99Xpv1EM_ubxpktX0T925-qej9fMEpzzQ5HLm
cNt1H2_VQ_Ww1JOLn9vRn-H48FDj7TxlIT74XdTZgTv31w_GRPAOfyxEw_ZUmxhz5Z-gTlQ",
       "kty": "RSA",
       "kid": "oauth-client"
     }
   ]
}

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

{
   "alg": "RS256",
   "d": "PjIX4i2NsBQuOVIw74ZDjqthYsoFvaoah9GP-cPrai5s5VUIlLoadEAdGbBrss
_6dR58x_pRlPHWh04vLQsFBuwQNc9SN3O6TAaai9Jg5TlCi6V0d4O6lUoTYpMR0cxFIU-xF
MwII--_OZRgmAxiYiAXQj7TKMKvgSvVO7-9-YdhMwHoD-UrJkfnZckMKSs0BoAbjReTski3
IV9f1wVJ53_pmr9NBpiZeHYmmG_1QDSbBuY35Zummut4QShF-fey2gSALdp9h9hRk1p1fsT
ZtH2lwpvmOcjwDkSDv-zO-4Pt8NuOyqNVPFahROBPlsMVxc_zjPck8ltblalBHPo6AQ",
   "e": "AQAB",
   "n": "kAMYD62n_f2rUcR4awJX4uccDt0zcXRssq_mDch5-ifcShx9aTtTVza23PTn3K
aKrsBXwWcfioXR6zQn5eYdZQVGNBfOR4rxF5i7t3hfb4WkS50EK1gBYk2lO9NSrQ-xG9QsU
sAnN6RHksXqsdOqv-nxjLexDfIJlgbcCN9h6TB-C66ZXv7PVhl19gIYVifSU7liHkLe0l0f
w7jUI6rHLHf4d96_neR1HrNIK_xssr99Xpv1EM_ubxpktX0T925-qej9fMEpzzQ5HLmcNt1
H2_VQ_Ww1JOLn9vRn-H48FDj7TxlIT74XdTZgTv31w_GRPAOfyxEw_ZUmxhz5Z-gTlQ",
   "kty": "RSA",
   "kid": "oauth-client"
}

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

2.4. Connection to the Protected Resource

2.4.1. Requests to the Protected Resource

Clients SHOULD send bearer tokens passed in the Authentication header as defined by [RFC6750] . Clients MAY use the form-parameter or query-parameter methods in [RFC6750] . 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:¶

GET /userinfo HTTP/1.1
Authorization: Bearer eyJhbGciOiJSUzI1NiJ9.eyJleHAiOjE0MTg3MDI0MTIsImF1ZCI6WyJjMWJjOD
RlNC00N2VlLTRiNjQtYmI1Mi01Y2RhNmM4MWY3ODgiXSwiaXNzIjoiaHR0cHM6XC9cL2lkcC1wLmV4YW1wbGU
uY29tXC8iLCJqdGkiOiJkM2Y3YjQ4Zi1iYzgxLTQwZWMtYTE0MC05NzRhZjc0YzRkZTMiLCJpYXQiOjE0MTg2
OTg4MTJ9.iHMz_tzZ90_b0QZS-AXtQtvclZ7M4uDAs1WxCFxpgBfBanolW37X8h1ECrUJexbXMD6rrj_uuWEq
PD738oWRo0rOnoKJAgbF1GhXPAYnN5pZRygWSD1a6RcmN85SxUig0H0e7drmdmRkPQgbl2wMhu-6h2Oqw-ize
4dKmykN9UX_2drXrooSxpRZqFVYX8PkCvCCBuFy2O-HPRov_SwtJMk5qjUWMyn2I4Nu2s-R20aCA-7T5dunr0
iWCkLQnVnaXMfA22RlRiU87nl21zappYb1_EHF9ePyq3Q353cDUY7vje8m2kKXYTgc_bUAYuW-W3SMSw5UlKa
HtSZ6PQICoA
Accept: text/plain, application/json, application/*+json, */*
Host: idp-p.example.com
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.2.3 (java 1.5)

3. Authorization Server Profile

All servers MUST conform to applicable recommendations found in the Security Considerations sections of [RFC6749] and those found in the OAuth Threat Model Document [RFC6819] .¶

The authorization server MUST protect all communications to and from its OAuth endpoints using TLS.¶

3.1. Connections with clients

3.1.1. Grant types

The authorization server MUST support the authorization_code , and MAY support the client_credentials grant types as described in Section 2 . The authorization server MUST limit each registered client (identified by a client ID) to a single grant type only, since a single piece of software will be functioning at runtime in only one of the modes described in Section 2 . Clients that have multiple modes of operation MUST have a separate client ID for each mode.¶

3.1.2. Client authentication

The authorization server MUST enforce client authentication as described above for the authorization code and client credentials grant types. Public client cannot authenticate to the authorization server.¶

The authorization server MUST validate all redirect URIs for authorization code and implicit grant types.¶

3.1.3. Dynamic Registration

Dynamic Registration allows for authorized Clients to on-board programatically 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 [RFC7591] 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 [RFC7591] 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:¶

redirect_uris: array of redirect URIs used by the client; subject to the requirements listed in Section 2.2.1 ¶
grant_types: grant type used by the client; must be "authorization_code" or "client_credentials"¶
jwks_uri or jwks: 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¶
client_name: human-readable name of the client¶
client_uri: URL of a web page containing further information about the client¶

3.1.4. Client Approval

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, or a public client.¶
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, for native clients a message indicating a new App installation has been registered as a client can help users determin if this is the expected behaviour. This signal helps users protect themselves fro potentially rogue clients.¶

3.1.5. Discovery

The authorization server MUST provide an OpenID Connect service discovery [OpenID.Discovery] endpoint listing the components relevant to the OAuth protocol:¶

issuer: REQUIRED. The fully qualified issuer URL of the server¶
authorization_endpoint: REQUIRED. The fully qualified URL of the server's authorization endpoint defined by OAuth 2.0 [RFC6749]¶
token_endpoint: REQUIRED. The fully qualified URL of the server's token endpoint defined by OAuth 2.0 [RFC6749]¶
introspection_endpoint: OPTIONAL. The fully qualified URL of the server's introspection endpoint defined by OAuth Token Introspection [RFC7662]¶
revocation_endpoint: OPTIONAL. The fully qualified URL of the server's revocation endpoint defined by OAuth 2.0 Token Revocation [RFC7009]¶
jwks_uri: REQUIRED. The fully qualified URI of the server's public key in JWK Set [RFC7517] format¶

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 the iGov OpenID Connect profile.¶

The following example shows the JSON document found at a discovery endpoint for an authorization server:¶

{
  "request_parameter_supported": true,
  "registration_endpoint": "https://idp-p.example.com/register",
  "userinfo_signing_alg_values_supported": [
    "HS256", "HS384", "HS512", "RS256", "RS384", "RS512"
  ],
  "token_endpoint": "https://idp-p.example.com/token",
  "request_uri_parameter_supported": false,
  "request_object_encryption_enc_values_supported": [
    "A192CBC-HS384", "A192GCM", "A256CBC+HS512",
    "A128CBC+HS256", "A256CBC-HS512",
    "A128CBC-HS256", "A128GCM", "A256GCM"
  ],
  "token_endpoint_auth_methods_supported": [
    "private_key_jwt",
  ],
  "jwks_uri": "https://idp-p.example.com/jwk",
  "authorization_endpoint": "https://idp-p.example.com/authorize",
  "require_request_uri_registration": false,
  "introspection_endpoint": "https://idp-p.example.com/introspect",
  "request_object_encryption_alg_values_supported": [
    "RSA-OAEP", ?RSA1_5", "RSA-OAEP-256"
  ],
  "service_documentation": "https://idp-p.example.com/about",
  "response_types_supported": [
    "code", "token"
  ],
  "token_endpoint_auth_signing_alg_values_supported": [
    "HS256", "HS384", "HS512", "RS256", "RS384", "RS512"
  ],
  "revocation_endpoint": "https://idp-p.example.com/revoke",
  "request_object_signing_alg_values_supported": [
    "HS256", "HS384", "HS512", "RS256", "RS384", "RS512"
  ],
  "grant_types_supported": [
    "authorization_code",
    "implicit",
    "urn:ietf:params:oauth:grant-type:jwt-bearer",
    "client_credentials",
    "urn:ietf:params:oauth:grant_type:redelegate"
  ],
  "scopes_supported": [
    "profile", "openid", "email", "address", "phone", "offline_access"
  ],
  "op_tos_uri": "https://idp-p.example.com/about",
  "issuer": "https://idp-p.example.com/",
  "op_policy_uri": "https://idp-p.example.com/about"
}

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. The key MUST contain the following fields:¶

kid: The key ID of the key pair used to sign this token¶
kty: The key type¶
alg: The default algorithm used for this key¶

The following is an example of a 2048-bit RSA public key:¶

{
  "keys": [
    {
      "alg": "RS256",
      "e": "AQAB",
      "n": "o80vbR0ZfMhjZWfqwPUGNkcIeUcweFyzB2S2T-hje83IOVct8gVg9FxvHPK1R
eEW3-p7-A8GNcLAuFP_8jPhiL6LyJC3F10aV9KPQFF-w6Eq6VtpEgYSfzvFegNiPtpMWd7C43
EDwjQ-GrXMVCLrBYxZC-P1ShyxVBOzeR_5MTC0JGiDTecr_2YT6o_3aE2SIJu4iNPgGh9Mnyx
dBo0Uf0TmrqEIabquXA1-V8iUihwfI8qjf3EujkYi7gXXelIo4_gipQYNjr4DBNlE0__RI0kD
U-27mb6esswnP2WgHZQPsk779fTcNDBIcYgyLujlcUATEqfCaPDNp00J6AbY6w",
      "kty": "RSA",
      "kid": "rsa1"
    }
  ]
}

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.¶

3.1.6. Revocation

Token revocation allows a client to signal to an authorization server that a given token will no longer be used.¶

An authorization server MUST revoke the 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 revocable.¶

A client MUST immediately discard the token and not use it again after revoking it.¶

3.1.7. PKCE

An authorization server MUST support the Proof Key for Code Exchange (PKCE [RFC7636]) extension to the authorization code flow, including support for the S256 code challenge method. The authorization server MUST NOT allow an iGov client to use the plain code challenge method.¶

3.1.8. Redirect URIs

The authorization server MUST compare a client's registered redirect URIs with the redirect URI presented during an authorization request using an exact string match.¶

3.1.9. RefreshTokens

Authorization Servers MAY issue refresh tokens to clients under the following context:¶

Clients MUST be registered with the Authorization Server.¶

Clients MUST present a valid client_id. COnfidential clients MUST present a signed client_assertion with their associated keypair.¶

Clients using the Direct Credentials method MUST NOT be issued refresh_tokens. These clients MUST present their client credentials with a new access_token request and the desired scope.¶

3.2. Connections with protected resources

Unlike the core OAuth protocol, the iGov profile intends to allow compliant protected resources to connect to compliant authorization servers.¶

3.2.1. JWT Bearer Tokens

In order to facilitate interoperability with multiple protected resources, all iGov-compliant authorization servers issue cryptographically signed tokens in the JSON Web Token (JWT) format. 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. When combined with discovery, this information is sufficient to programmatically locate the token introspection service, which is in turn used for conveying additional security information about the token.¶

The server MUST issue tokens as JWTs with, at minimum, the following claims:¶

iss: The issuer URL of the server that issued the token¶
azp: The client id of the client to whom this token was issued¶
exp: The expiration time (integer number of seconds since from 1970-01-01T00:00:00Z UTC), after which the token MUST be considered invalid¶
jti: 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 additional fields, including the following as defined here:¶

sub: 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 audiance requires otherwise.¶
aud: 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 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:¶

{
   "exp": 1418702388,
   "azp": "55f9f559-2496-49d4-b6c3-351a586b7484",
   "iss": "https://idp-p.example.com/",
   "jti": "2402f87c-b6ce-45c4-95b0-7a3f2904997f",
   "iat": 1418698788
}

The access tokens MUST be signed with JWS [RFC7515] . 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 [JWS.JWE.Algs] . The JWS header MUST contain the following fields:¶

kid: 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:¶

eyJhbGciOiJSUzI1NiJ9.ew0KICAgImV4cCI6IDE0MTg3MDIzODgsDQogICAiYXpwIjo
gIjU1ZjlmNTU5LTI0OTYtNDlkNC1iNmMzLTM1MWE1ODZiNzQ4NCIsDQogICAiaXNzIjo
gImh0dHBzOi8vaWRwLXAuZXhhbXBsZS5jb20vIiwNCiAgICJqdGkiOiAiMjQwMmY4N2M
tYjZjZS00NWM0LTk1YjAtN2EzZjI5MDQ5OTdmIiwNCiAgICJpYXQiOiAxNDE4Njk4Nzg
4LA0KICAgImtpZCI6ICJyc2ExIg0KfQ.iB6Ix8Xeg-L-nMStgE1X75w7zgXabzw7znWU
ECOsXpHfnYYqb-CET9Ah5IQyXIDZ20qEyN98UydgsTpiO1YJDDcZV4f4DgY0ZdG3yBW3
XqwUQwbgF7Gwza9Z4AdhjHjzQx-lChXAyfL1xz0SBDkVbJdDjtXbvaSIyfF7ueWF3M1C
M70-GXuRY4iucKbuytz9e7eW4Egkk4Aagl3iTk9-l5V-tvL6dYu8IlR93GKsaKE8bng0
EZ04xcnq8s4V5Yykuc_NARBJENiKTJM8w3wh7xWP2gvMp39Y0XnuCOLyIx-J1ttX83xm
pXDaLyyY-4HT9XHT9V73fKF8rLWJu9grrA

Refresh tokens SHOULD be signed with JWS [RFC7515] 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 [RFC7516] . 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.¶

3.2.2. Introspection

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:¶

POST /introspect HTTP/1.1
User-Agent: Faraday v0.9.0
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip;q=1.0,deflate;q=0.6,identity;q=0.3
Accept: */*
Connection: close
Host: as-va.example.com
Content-Length: 1412

client_assertion=eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.eyJpc3M
iOiJhMmMzNjkxOS0wMWZmLTQ4MTAtYTgyOS00MDBmYWQzNTczNTEiLCJzdWIi
OiJhMmMzNjkxOS0wMWZmLTQ4MTAtYTgyOS00MDBmYWQzNTczNTEiLCJhdWQiO
iJodHRwczovL2FzLXZhLmV4YW1wbGUuY29tL3Rva2VuIiwiaWF0IjoxNDE4Nj
k4ODE0LCJleHAiOjE0MTg2OTg4NzQsImp0aSI6IjE0MTg2OTg4MTQvZmNmNDQ
2OGY2MDVjNjE1NjliOWYyNGY5ODJlMTZhZWY2OTU4In0.md7mFdNBaGhiJfE_
pFkAAWA5S-JBvDw9Dk7pOOJEWcL08JGgDFoi9UDbg3sHeA5DrrCYGC_zw7fCG
c9ovpfMB7W6YN53hGU19LtzzFN3tv9FNRq4KIzhK15pns9jckKtui3HZ25L_B
-BnxHe7xNo3kA1M-p51uYYIM0hw1SRi2pfwBKG5O8WntybLjuJ0R3X97zvqHn
2Q7xdVyKlInyNPA8gIZK0HVssXxHOI6yRrAqvdMn_sneDTWPrqVpaR_c7rt8D
dd7drf_nTD1QxESVhYqKTax5Qfd-aq8gZz8gJCzS0yyfQh6DmdhmwgrSCCRC6
BUQkeFNvjMVEYHQ9fr0NA
&client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_id=a2c36919-01ff-4810-a829-400fad357351
&token=eyJhbGciOiJSUzI1NiJ9.eyJleHAiOjE0MTg3MDI0MTQsImF1ZCI6W
yJlNzFmYjcyYS05NzRmLTQwMDEtYmNiNy1lNjdjMmJjMDAzN2YiXSwiaXNzIj
oiaHR0cHM6XC9cL2FzLXZhLmV4YW1wbGUuY29tXC8iLCJqdGkiOiIyMWIxNTk
2ZC04NWQzLTQzN2MtYWQ4My1iM2YyY2UyNDcyNDQiLCJpYXQiOjE0MTg2OTg4
MTR9.FXDtEzDLbTHzFNroW7w27RLk5m0wprFfFH7h4bdFw5fR3pwiqejKmdfA
bJvN3_yfAokBv06we5RARJUbdjmFFfRRW23cMbpGQCIk7Nq4L012X_1J4IewO
QXXMLTyWQQ_BcBMjcW3MtPrY1AoOcfBOJPx1k2jwRkYtyVTLWlff6S5gK-ciY
f3b0bAdjoQEHd_IvssIPH3xuBJkmtkrTlfWR0Q0pdpeyVePkMSI28XZvDaGnx
A4j7QI5loZYeyzGR9h70xQLVzqwwl1P0-F_0JaDFMJFO1yl4IexfpoZZsB3Hh
F2vFdL6D_lLeHRy-H2g2OzF59eMIsM_Ccs4G47862w

The client assertion parameter is structured as described in Section 2.3.2 .¶

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:¶

active: 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.¶
scope: Space-separated list of OAuth 2.0 scope values represented as a single string.¶
exp: Timestamp of when this token expires (integer number of seconds since from 1970-01-01T00:00:00Z UTC)¶
sub: 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.¶
client_id: 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:¶

HTTP/1.1 200 OK
Date: Tue, 16 Dec 2014 03:00:14 GMT
Access-Control-Allow-Origin: *
Content-Type: application/json;charset=ISO-8859-1
Content-Language: en-US
Content-Length: 266
Connection: close

{
   "active": true,
   "scope": "file search visa",
   "exp": 1418702414,
   "sub": "{sub\u003d6WZQPpnQxV, iss\u003dhttps://idp-p.example.com/}",
   "client_id": "e71fb72a-974f-4001-bcb7-e67c2bc0037f",
   "token_type": "Bearer"
}

The authorization server MUST require authentication for both the revocation and introspection endpoints as described in Section 2.3.2 . 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.¶

3.3. Response to Authorization Requests

The following data will be sent as an Authorization Response to the Authorization Code Flow as desribed above. The authentication response is sent via HTTP redirect to the redirect URI specified in the request.¶

The following fields MUST be included in the response:¶

state: REQUIRED. The value of the state parameter passed in in the authentication request. This value MUST match exactly.¶
code: 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 "code" as per Section 4.4 of Proof Key for Code Exchange by OAuth Public Clients (PKCE) [RFC7636]¶

The following is an example response:¶

https://https://client.example.org/cb?
    state=2ca3359dfbfd0
   &code=gOIFJ1hV6Rb1sxUdFhZGACWwR1sMhYbJJcQbVJN0wHA

3.4. Token Lifetimes

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 public clients 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.¶

3.5. Scopes

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.¶

4. Protected Resource Profile

4.1. Protecting Resources

Protected Resources grant access to clients if they present a valid access_token with the appropriate scope. 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 that require a higher end-user authentication trust level to access certain resources MUST associate those resources with a unique scope.¶

Clients wishing access to these higher level resources MUST include the higher level scope in their authorization request to the authorization server.¶

Authorization servers MUST authenitcate the end-user with the appropriate trust level before providing an authorization_code or associated access_token to the client.¶

Authorization servers MUST only grant access to higher level scope resources to clients that have permission to request these scope levels. Client authorization requests containing scopes that are outside their permisson MUST be rejected.¶

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 additonal user authentication/authorization.¶

For example: a resource server has resources classified as "public" and "sensitive". "Sensitive" resources require the user to perform a two-factor authentication, and those access grants are short-lived: 15 minutes. For a client to obtain access to both "public" and "sensitive" resources, it makes an authorization request to the authorization server with scope=public+sensitive. 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 15mins, and a refresh_token for the "public" scope with an expiry time of 24 hrs. The client can access both "public" and "sensitive" resources for 15mins with the access_token. When the access_token expires, the client will NOT be able to access "public" or "sensitive" resources any longer as the access_token has expired, and must obtain a new access_token. The client makes a access grant request (as described in OAuth 2.0 [RFC6749] 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" scopewith 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.¶

4.2. Connections with Clients

A protected resource MUST accept bearer tokens passed in the authorization header as described in [RFC6750] . A protected resource MAY also accept bearer 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.¶

4.3. Connections with Authorization Servers

Protected resources MUST interpret access tokens using either JWT, token introspection, or a combination of the two.¶

The protected resource MUST check the aud (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 and acr associated with the token from the authorization server's token introspection endpoint.¶

A protected resource 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.¶

International Government Assurance Profile (iGov) for OAuth 2.0 - draft 04