OAuth 2.0 Authorization Code Flow UI Implementation Design

OAuth 2.0 Authorization Code Flow UI Implementation Design

Version: 1.2 Status: Design + implementation notes Date: February 2026 Related: OAuth Design Document

Executive Summary

This document describes how the Admin UI initiates OAuth 2.0 Authorization Code flow for MCP gateways and how the backend stores and uses user-delegated tokens. It reflects current behavior in code and calls out remaining gaps.

!!! note "Scope of This Document" This document covers the UI implementation for gateway OAuth token delegation - specifically how administrators configure OAuth settings and authorize access to upstream MCP servers.

For information about **user authentication to MCP Gateway** (SSO, JWT tokens, RBAC), see:

- [RBAC Configuration](../manage/rbac.md) - Token scoping, permissions, and access control
- [Multi-Tenancy Architecture](./multitenancy.md) - User authentication flows and team management

Current Implementation Snapshot

Implemented today

• Admin UI exposes OAuth configuration fields for gateways and an "Authorize" action.
• Authorization Code flow uses PKCE (S256) and an HMAC-signed state value with a 300-second TTL.
• OAuth state is stored in Redis when CACHE_TYPE=redis, in the database when CACHE_TYPE=database, and in memory otherwise.
• Tokens are stored per gateway and app user (email) in oauth_tokens, encrypted with AUTH_ENCRYPTION_SECRET.
• Refresh tokens are used when access tokens are near expiry; invalid refresh tokens are cleared.
• DCR auto-registration can run during /oauth/authorize/{gateway_id} when issuer is set and client_id is missing.

Known gaps and constraints

• oauth_store_tokens and oauth_auto_refresh checkboxes exist in the UI but are not persisted or enforced by the backend.
• OAUTH_PREFERRED_CODE_CHALLENGE_METHOD is defined but PKCE is always S256 today.
• No admin UI to list or revoke stored OAuth tokens per user.
• Token cleanup is a helper method only; there is no scheduler invoking it.

Architecture Overview

graph TD
    subgraph "Admin UI"
        A[Gateway OAuth Configuration]
        B[Authorize Button]
    end

    subgraph "Backend"
        C[OAuth Router]
        D[OAuth Manager]
        E[Token Storage Service]
    end

    subgraph "State Store"
        S[Redis / Database / Memory]
    end

    subgraph "Database"
        G[gateways.oauth_config]
        T[oauth_tokens]
        ST[oauth_states when CACHE_TYPE=database]
    end

    subgraph "External"
        U[User Browser]
        O[OAuth Provider]
    end

    A --> G
    B --> C
    C --> D
    D --> S
    D --> O
    O --> C
    C --> E
    E --> T
    E --> ST
    B --> U
    U --> O

Authorize redirects to /oauth/authorize/{gateway_id}. The OAuth Manager performs PKCE and state handling.

Data Model

Gateway OAuth configuration (gateways.oauth_config)

Stored as JSON and assembled from Admin UI fields or API payloads.

• grant_type: authorization_code, client_credentials, or password
• issuer: OAuth Authorization Server issuer URL (required for DCR)
• authorization_url: OAuth authorization endpoint
• token_url: OAuth token endpoint
• redirect_uri: Must match the OAuth client registration
• client_id: OAuth client identifier
• client_secret: Encrypted before storage
• username / password: Used only for password grant
• scopes: Array of requested scopes
• resource (optional): RFC 8707 resource parameter; when omitted, /oauth/authorize derives it from the gateway URL

oauth_tokens

One token record per gateway and app user (email).

• gateway_id, app_user_email (unique pair)
• user_id (OAuth provider user identifier)
• access_token, refresh_token (encrypted at rest)
• token_type, expires_at, scopes
• created_at, updated_at

oauth_states (database-backed state storage)

Used only when CACHE_TYPE=database.

• gateway_id, state (unique)
• code_verifier (PKCE)
• expires_at, used, created_at
• TTL is enforced in logic (300 seconds)

registered_oauth_clients (DCR, optional)

Stored when Dynamic Client Registration succeeds.

• issuer, client_id, client_secret_encrypted
• redirect_uris, grant_types, response_types, scope
• token_endpoint_auth_method, registration_client_uri
• created_at, expires_at, is_active

UI and Flow

Admin UI touchpoints

The gateway form maps these inputs into oauth_config:

• oauth_grant_type
• oauth_issuer
• oauth_client_id
• oauth_client_secret
• oauth_authorization_url
• oauth_token_url
• oauth_redirect_uri
• oauth_scopes
• oauth_username / oauth_password (password grant only)

The gateway list shows an Authorize button for OAuth gateways, which sends the current user through /oauth/authorize/{gateway_id}.

Authorization Code flow (current)

sequenceDiagram
    participant Admin
    participant UI as Admin UI
    participant Gateway as OAuth Router (/oauth/authorize)
    participant OAuthMgr as OAuth Manager
    participant StateStore as State Store
    participant Provider as OAuth Provider
    participant TokenStore as Token Storage Service
    participant DB as Database

    Admin->>UI: Configure gateway OAuth settings
    UI->>DB: Save oauth_config in gateways

    Admin->>UI: Click "Authorize"
    UI->>Gateway: GET /oauth/authorize/{gateway_id}
    Gateway->>OAuthMgr: Initiate auth code flow (PKCE)
    OAuthMgr->>StateStore: Store state + code_verifier (TTL 300s)
    OAuthMgr-->>Gateway: Authorization URL
    Gateway-->>Admin: Redirect to provider

    Admin->>Provider: Login + consent
    Provider-->>Gateway: Redirect /oauth/callback?code&state
    Gateway->>OAuthMgr: Validate state + exchange code
    OAuthMgr->>Provider: POST /token (code + code_verifier)
    Provider-->>OAuthMgr: access_token + refresh_token
    OAuthMgr->>TokenStore: Store tokens for app_user_email
    TokenStore->>DB: Upsert oauth_tokens
    Gateway-->>Admin: Success page

Tool invocation using stored tokens

sequenceDiagram
    participant Client as MCP Client (authenticated user)
    participant Gateway
    participant TokenStore as Token Storage Service
    participant Provider as OAuth Provider
    participant MCP as MCP Server

    Client->>Gateway: Invoke tool
    Gateway->>TokenStore: Get token for gateway + app_user_email
    TokenStore->>TokenStore: Check expiration

    alt Token valid
        TokenStore-->>Gateway: Decrypted access token
        Gateway->>MCP: Tool request + Bearer token
        MCP-->>Gateway: Tool response
        Gateway-->>Client: Result
    else Token expired
        TokenStore->>Provider: Refresh token request
        Provider-->>TokenStore: New access token
        TokenStore->>DB: Update oauth_tokens
        TokenStore-->>Gateway: New access token
        Gateway->>MCP: Tool request + Bearer token
        MCP-->>Gateway: Tool response
        Gateway-->>Client: Result
    end

Security and Operational Notes

• Tokens are encrypted at rest using AUTH_ENCRYPTION_SECRET (via the encryption service).
• State is HMAC-signed with AUTH_ENCRYPTION_SECRET, single-use, and expires after 300 seconds.
• Tokens are scoped per gateway and app user (email); cross-user reuse is blocked.
• The gateway derives an RFC 8707 resource value from the gateway URL when oauth_config.resource is absent.
• HTTPS is recommended in production; the gateway does not enforce it automatically.

Relationship to Gateway Authentication

This OAuth flow is for upstream server authentication and is separate from user authentication to the MCP Gateway:

For user authentication and RBAC configuration, see RBAC Configuration.

Configuration

Validation Checklist

• Create an OAuth gateway with authorization_code grant and complete provider consent via Authorize.
• Confirm an oauth_tokens record exists for your user and gateway.
• Invoke a tool to verify the stored token is used.
• Let the access token expire and confirm refresh happens when a refresh token is available.
• Switch CACHE_TYPE between database and redis to confirm state storage works in both modes.

Future Enhancements

• Wire oauth_store_tokens and oauth_auto_refresh to backend behavior.
• Make PKCE method configurable using OAUTH_PREFERRED_CODE_CHALLENGE_METHOD.
• Add admin UI for token status and revocation.
• Schedule periodic cleanup of expired OAuth tokens.