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* OAuth Authentication Middleware
*
* Validates Bearer tokens on MCP endpoints and sets up the token context
* for per-request GitLab API access.
*
* This middleware:
* 1. Extracts and validates the Bearer token from Authorization header
* 2. Verifies the JWT signature and expiration
* 3. Loads the associated session
* 4. Refreshes GitLab token if needed
* 5. Sets up token context for the request
*/
import { Request, Response, NextFunction } from "express";
import { loadOAuthConfig } from "../oauth/config";
import { sessionStore } from "../oauth/session-store";
import { verifyMCPToken, isTokenExpiringSoon, calculateTokenExpiry } from "../oauth/token-utils";
import { runWithTokenContext } from "../oauth/token-context";
import { refreshGitLabToken } from "../oauth/gitlab-device-flow";
import { logger } from "../logger";
import { OAuthErrorResponse } from "../oauth/types";
/**
* OAuth authentication middleware for Express
*
* Apply this middleware to routes that require OAuth authentication.
* It validates the Bearer token and sets up the token context.
*
* @param req - Express request
* @param res - Express response
* @param next - Express next function
*/
export async function oauthAuthMiddleware(
req: Request,
res: Response,
next: NextFunction
): Promise<void> {
const config = loadOAuthConfig();
if (!config) {
sendUnauthorized(res, "server_error", "OAuth not configured");
return;
}
// Extract Bearer token from Authorization header
const authHeader = req.headers.authorization;
if (!authHeader) {
sendUnauthorized(res, "unauthorized", "Missing Authorization header");
return;
}
if (!authHeader.startsWith("Bearer ")) {
sendUnauthorized(
res,
"unauthorized",
"Invalid Authorization header format. Expected: Bearer <token>"
);
return;
}
const token = authHeader.slice(7); // Remove "Bearer " prefix
if (!token) {
sendUnauthorized(res, "unauthorized", "Empty Bearer token");
return;
}
// Verify JWT token
const payload = verifyMCPToken(token, config.sessionSecret);
if (!payload) {
sendUnauthorized(res, "invalid_token", "Token is invalid or expired");
return;
}
// Get session from token
const sessionId = payload.sid;
const session = sessionStore.getSession(sessionId);
if (!session) {
sendUnauthorized(res, "invalid_token", "Session not found or expired");
return;
}
// Verify token matches session
if (session.mcpAccessToken !== token) {
// Token might have been rotated
sendUnauthorized(res, "invalid_token", "Token has been superseded");
return;
}
// Refresh GitLab token if it's expiring soon (5 minute buffer)
if (isTokenExpiringSoon(session.gitlabTokenExpiry)) {
try {
const newTokens = await refreshGitLabToken(session.gitlabRefreshToken, config);
sessionStore.updateSession(sessionId, {
gitlabAccessToken: newTokens.access_token,
gitlabRefreshToken: newTokens.refresh_token,
gitlabTokenExpiry: calculateTokenExpiry(newTokens.expires_in),
});
logger.debug(
{ sessionId: sessionId.substring(0, 8) + "..." },
"GitLab token refreshed during request"
);
} catch (error: unknown) {
logger.error({ err: error as Error }, "Failed to refresh GitLab token during request");
sendUnauthorized(
res,
"invalid_token",
"GitLab token refresh failed. Please re-authenticate."
);
return;
}
}
// Get potentially updated session
const updatedSession = sessionStore.getSession(sessionId);
if (!updatedSession) {
sendUnauthorized(res, "invalid_token", "Session lost during token refresh");
return;
}
// Set up token context and continue
// All code in the request handler will have access to the GitLab token via getGitLabTokenFromContext()
try {
await runWithTokenContext(
{
gitlabToken: updatedSession.gitlabAccessToken,
gitlabUserId: updatedSession.gitlabUserId,
gitlabUsername: updatedSession.gitlabUsername,
sessionId: updatedSession.id,
},
async () => {
// Call next() inside the context so all downstream code has access to the token
next();
}
);
} catch (error: unknown) {
logger.error({ err: error as Error }, "Error in OAuth-authenticated request");
throw error;
}
}
/**
* Create OAuth middleware for specific routes
*
* Returns the middleware function configured for OAuth authentication.
* Use this when you need to programmatically apply the middleware.
*/
export function createOAuthMiddleware(): typeof oauthAuthMiddleware {
return oauthAuthMiddleware;
}
/**
* Optional OAuth middleware
*
* Like oauthAuthMiddleware, but doesn't require authentication.
* If a valid token is provided, sets up the context.
* If no token or invalid token, continues without context.
*
* Useful for endpoints that work with or without authentication.
*/
export async function optionalOAuthMiddleware(
req: Request,
res: Response,
next: NextFunction
): Promise<void> {
const config = loadOAuthConfig();
if (!config) {
// OAuth not configured, continue without context
next();
return;
}
const authHeader = req.headers.authorization;
if (!authHeader?.startsWith("Bearer ")) {
// No token provided, continue without context
next();
return;
}
const token = authHeader.slice(7);
if (!token) {
next();
return;
}
// Try to validate token
const payload = verifyMCPToken(token, config.sessionSecret);
if (!payload) {
// Invalid token, but this is optional auth, so continue
next();
return;
}
const session = sessionStore.getSession(payload.sid);
if (session?.mcpAccessToken !== token) {
next();
return;
}
// Valid token - set up context
try {
await runWithTokenContext(
{
gitlabToken: session.gitlabAccessToken,
gitlabUserId: session.gitlabUserId,
gitlabUsername: session.gitlabUsername,
sessionId: session.id,
},
async () => {
next();
}
);
} catch (error: unknown) {
logger.error({ err: error as Error }, "Error in optional OAuth request");
throw error;
}
}
/**
* Send unauthorized response with OAuth error format
*/
function sendUnauthorized(res: Response, error: string, description: string): void {
const response: OAuthErrorResponse = {
error,
error_description: description,
};
// Set WWW-Authenticate header as per OAuth spec
res.setHeader("WWW-Authenticate", 'Bearer realm="gitlab-mcp"');
res.status(401).json(response);
}
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