OAuth 2.0

Authrim implements OAuth 2.0 with modern security best practices, including support for OAuth 2.1 recommendations.

Overview

Standards: RFC 6749, RFC 6750
OAuth 2.1: Aligned with OAuth 2.1 draft
Security: Following OAuth Security BCP

Supported Grant Types

Authorization Code Grant

The recommended grant for all clients:

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code
&code=auth_code_value
&redirect_uri=https://app.example.com/callback
&client_id=client_id
&code_verifier=pkce_verifier

Refresh Token Grant

Exchange a refresh token for new tokens:

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Authorization: Basic <base64(client_id:client_secret)>

grant_type=refresh_token
&refresh_token=refresh_token_value

Client Credentials Grant

For machine-to-machine authentication:

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Authorization: Basic <base64(client_id:client_secret)>

grant_type=client_credentials
&scope=api.read api.write

Device Authorization Grant

For input-constrained devices (see Device Flow):

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded

grant_type=urn:ietf:params:oauth:grant-type:device_code
&device_code=device_code_value
&client_id=client_id

JWT Bearer Grant

For identity federation with trusted assertion issuers:

POST /token HTTP/1.1
Content-Type: application/x-www-form-urlencoded

grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer
&assertion=jwt_assertion
&client_id=client_id

Endpoints

Endpoint	Method	Description
`/authorize`	GET/POST	Authorization endpoint
`/token`	POST	Token endpoint
`/revoke`	POST	Token revocation
`/introspect`	POST	Token introspection

Token Types

Access Tokens

JWT-formatted access tokens containing:

{
  "iss": "https://auth.example.com",
  "sub": "user-id-123",
  "aud": "https://api.example.com",
  "exp": 1699880000,
  "iat": 1699876400,
  "jti": "unique-token-id",
  "scope": "read write",
  "client_id": "my_client_id"
}

Refresh Tokens

Long-lived tokens for obtaining new access tokens:

Rotation: Refresh tokens are rotated on each use
Expiration: Configurable lifetime (default: 30 days)
Revocation: Can be revoked via /revoke endpoint

Client Authentication

client_secret_basic

HTTP Basic authentication with client credentials:

Authorization: Basic <base64(client_id:client_secret)>

client_secret_post

Client credentials in request body:

POST /token
Content-Type: application/x-www-form-urlencoded

client_id=my_client_id
&client_secret=my_client_secret
&grant_type=...

private_key_jwt

JWT client assertion signed with client’s private key:

POST /token
Content-Type: application/x-www-form-urlencoded

client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiJ9...
&grant_type=...

none

For public clients (must use PKCE):

POST /token
Content-Type: application/x-www-form-urlencoded

client_id=public_client_id
&grant_type=authorization_code
&code=...
&code_verifier=...

Token Introspection

Check if a token is active and get its metadata:

POST /introspect HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Authorization: Basic <base64(client_id:client_secret)>

token=access_token_value
&token_type_hint=access_token

Response:

{
  "active": true,
  "scope": "read write",
  "client_id": "my_client_id",
  "username": "[email protected]",
  "token_type": "Bearer",
  "exp": 1699880000,
  "iat": 1699876400,
  "sub": "user-id-123",
  "aud": "https://api.example.com",
  "iss": "https://auth.example.com"
}

Token Revocation

Revoke an access token or refresh token:

POST /revoke HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Authorization: Basic <base64(client_id:client_secret)>

token=token_value
&token_type_hint=refresh_token

Response: 200 OK (always, per RFC 7009)

Response Modes

query (default for code)

Authorization code in query string:

https://app.example.com/callback?code=abc123&state=xyz

fragment (default for implicit)

Token in URL fragment:

https://app.example.com/callback#access_token=abc123&token_type=Bearer

form_post

Authorization response submitted via POST:

<form method="post" action="https://app.example.com/callback">
  <input type="hidden" name="code" value="abc123">
  <input type="hidden" name="state" value="xyz">
</form>

Error Responses

Standard OAuth 2.0 error format:

{
  "error": "invalid_request",
  "error_description": "The request is missing a required parameter"
}

Error Codes:

Error	Description
`invalid_request`	Missing or invalid parameter
`unauthorized_client`	Client not authorized for grant type
`access_denied`	User denied authorization
`unsupported_response_type`	Response type not supported
`invalid_scope`	Requested scope is invalid
`server_error`	Server encountered an error
`temporarily_unavailable`	Server is temporarily unavailable
`invalid_client`	Client authentication failed
`invalid_grant`	Grant is invalid or expired
`unsupported_grant_type`	Grant type not supported

OAuth 2.1 Alignment

Authrim follows OAuth 2.1 recommendations:

PKCE required for authorization code flow
Refresh token rotation enabled by default
No implicit grant for new applications
No password grant (removed)
Exact redirect URI matching

Security Best Practices

Use PKCE - Required for all authorization code flows
Use state parameter - Prevent CSRF attacks
Validate redirect URIs - Exact matching only
Use short-lived access tokens - 1 hour or less
Rotate refresh tokens - One-time use
Implement token binding - Consider DPoP for high-security