OpenID Connect (OIDC) with ruby-oauth/oauth2
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OIDC Libraries
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Libraries built on top of the oauth2 gem that implement OIDC.
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If any other libraries would like to be added to this list, please open an issue or pull request.
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Raw OIDC with ruby-oauth/oauth2
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This document complements the inline documentation by focusing on OpenID Connect (OIDC) 1.0 usage patterns when using this gem as an OAuth 2.0 client library.
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Scope of this document
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+ - Audience: Developers building an OAuth 2.0/OIDC Relying Party (RP, aka client) in Ruby.
+ - Non-goals: This gem does not implement an OIDC Provider (OP, aka Authorization Server); for OP/server see other projects (e.g., doorkeeper + oidc extensions).
+ - Status: Informational documentation with links to normative specs. The gem intentionally remains protocol-agnostic beyond OAuth 2.0; OIDC specifics (like ID Token validation) must be handled by your application.
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+
Key concepts refresher
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+ - OAuth 2.0 delegates authorization; it does not define authentication of the end-user.
+ - OIDC layers an identity layer on top of OAuth 2.0, introducing:
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+ - ID Token: a JWT carrying claims about the authenticated end-user and the authentication event.
+ - Standardized scopes: openid (mandatory), profile, email, address, phone, offline_access, and others.
+ - UserInfo endpoint: a protected resource for retrieving user profile claims.
+ - Discovery and Dynamic Client Registration (optional for providers/clients that support them).
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What this gem provides for OIDC
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+ - All OAuth 2.0 client capabilities required for OIDC flows: building authorization requests, exchanging authorization codes, refreshing tokens, and making authenticated resource requests.
+ - Transport and parsing conveniences (snaky hash, Faraday integration, error handling, etc.).
+ - Optional client authentication schemes useful with OIDC deployments:
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+ - basic_auth (default)
+ - request_body (legacy)
+ - tls_client_auth (MTLS)
+ - private_key_jwt (OIDC-compliant when configured per OP requirements)
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What you must add in your app for OIDC
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+ - ID Token validation: This gem surfaces id_token values but does not verify them. Your app should:
+1) Parse the JWT (header, payload, signature)
+2) Fetch the OP JSON Web Key Set (JWKS) from discovery (or configure statically)
+3) Select the correct key by kid (when present) and verify the signature and algorithm
+4) Validate standard claims (iss, aud, exp, iat, nbf, azp, nonce when used, at_hash/c_hash when applicable)
+5) Enforce expected client_id, issuer, and clock skew policies
+ - Nonce handling for Authorization Code flow with OIDC: generate a cryptographically-random nonce, bind it to the user session before redirect, include it in authorize request, and verify it in the ID Token on return.
+ - PKCE is best practice and often required by OPs: generate/verifier, send challenge in authorize, send verifier in token request.
+ - Session/state management: continue to validate state to mitigate CSRF; use exact redirect_uri matching.
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Minimal OIDC Authorization Code example
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require "oauth2"
+require "jwt" # jwt/ruby-jwt
+require "net/http"
+require "json"
+
+client = OAuth2::Client.new(
+ ENV.fetch("OIDC_CLIENT_ID"),
+ ENV.fetch("OIDC_CLIENT_SECRET"),
+ site: ENV.fetch("OIDC_ISSUER"), # e.g. https://accounts.example.com
+ authorize_url: "/authorize", # or discovered
+ token_url: "/token", # or discovered
+)
+
+# Step 1: Redirect to OP for consent/auth
+state = SecureRandom.hex(16)
+nonce = SecureRandom.hex(16)
+pkce_verifier = SecureRandom.urlsafe_base64(64)
+pkce_challenge = Base64.urlsafe_encode64(Digest::SHA256.digest(pkce_verifier)).delete("=")
+
+authz_url = client.auth_code.authorize_url(
+ scope: "openid profile email",
+ state: state,
+ nonce: nonce,
+ code_challenge: pkce_challenge,
+ code_challenge_method: "S256",
+ redirect_uri: ENV.fetch("OIDC_REDIRECT_URI"),
+)
+# redirect_to authz_url
+
+# Step 2: Handle callback
+# params[:code], params[:state]
+raise "state mismatch" unless params[:state] == state
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+token = client.auth_code.get_token(
+ params[:code],
+ redirect_uri: ENV.fetch("OIDC_REDIRECT_URI"),
+ code_verifier: pkce_verifier,
+)
+
+# The token may include: access_token, id_token, refresh_token, etc.
+id_token = token.params["id_token"] || token.params[:id_token]
+
+# Step 3: Validate the ID Token (simplified – add your own checks!)
+# Discover keys (example using .well-known)
+issuer = ENV.fetch("OIDC_ISSUER")
+jwks_uri = JSON.parse(Net::HTTP.get(URI.join(issuer, "/.well-known/openid-configuration"))).
+ fetch("jwks_uri")
+jwks = JSON.parse(Net::HTTP.get(URI(jwks_uri)))
+keys = jwks.fetch("keys")
+
+# Use ruby-jwt JWK loader
+jwk_set = JWT::JWK::Set.new(keys.map { |k| JWT::JWK.import(k) })
+
+decoded, headers = JWT.decode(
+ id_token,
+ nil,
+ true,
+ algorithms: ["RS256", "ES256", "PS256"],
+ jwks: jwk_set,
+ verify_iss: true,
+ iss: issuer,
+ verify_aud: true,
+ aud: ENV.fetch("OIDC_CLIENT_ID"),
+)
+
+# Verify nonce
+raise "nonce mismatch" unless decoded["nonce"] == nonce
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+# Optionally: call UserInfo
+userinfo = token.get("/userinfo").parsed
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Notes on discovery and registration
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+ - Discovery: Most OPs publish configuration at issuer/.well-known/openid-configuration (OIDC Discovery 1.0). From there, resolve authorization_endpoint, token_endpoint, jwks_uri, userinfo_endpoint, etc.
+ - Dynamic Client Registration: Some OPs allow registering clients programmatically (OIDC Dynamic Client Registration 1.0). This gem does not implement registration; use a plain HTTP client or Faraday and store credentials securely.
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Common pitfalls and tips
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+ - Always request the openid scope when you expect an ID Token. Without it, the OP may behave as vanilla OAuth 2.0.
+ - Validate ID Token signature and claims before trusting any identity data. Do not rely solely on the presence of an id_token field.
+ - Prefer Authorization Code + PKCE. Avoid Implicit; it is discouraged in modern guidance and may be disabled by providers.
+ - Use exact redirect_uri matching, and keep your allow-list short.
+ - For public clients that use refresh tokens, prefer sender-constrained tokens (DPoP/MTLS) or rotation with one-time-use refresh tokens, per modern best practices.
+ - When using private_key_jwt, ensure the “aud” (or token_url) and “iss/sub” claims are set per the OP’s rules, and include kid in the JWT header when required so the OP can select the right key.
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Relevant specifications and references
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+ - OpenID Connect Core 1.0: https://openid.net/specs/openid-connect-core-1_0.html
+ - OIDC Core (final): https://openid.net/specs/openid-connect-core-1_0-final.html
+ - How OIDC works: https://openid.net/developers/how-connect-works/
+ - OpenID Connect home: https://openid.net/connect/
+ - OIDC Discovery 1.0: https://openid.net/specs/openid-connect-discovery-1_0.html
+ - OIDC Dynamic Client Registration 1.0: https://openid.net/specs/openid-connect-registration-1_0.html
+ - OIDC Session Management 1.0: https://openid.net/specs/openid-connect-session-1_0.html
+ - OIDC RP-Initiated Logout 1.0: https://openid.net/specs/openid-connect-rpinitiated-1_0.html
+ - OIDC Back-Channel Logout 1.0: https://openid.net/specs/openid-connect-backchannel-1_0.html
+ - OIDC Front-Channel Logout 1.0: https://openid.net/specs/openid-connect-frontchannel-1_0.html
+ - Auth0 OIDC overview: https://auth0.com/docs/authenticate/protocols/openid-connect-protocol
+ - Spring Authorization Server’s list of OAuth2/OIDC specs: https://github.com/spring-projects/spring-authorization-server/wiki/OAuth2-and-OIDC-Specifications
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See also
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+ - README sections on OAuth 2.1 notes and OIDC notes
+ - Strategy classes under lib/oauth2/strategy for flow helpers
+ - Specs under spec/oauth2 for concrete usage patterns
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Contributions welcome
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+ - If you discover provider-specific nuances, consider contributing examples or clarifications (without embedding provider-specific hacks into the library).
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