From 9dc4a4f6a91052def706eba888f6ec072351d6bb Mon Sep 17 00:00:00 2001
From: Justin Spahr-Summers <justin@anthropic.com>
Date: Mon, 17 Feb 2025 14:37:10 +0000
Subject: [PATCH] WIP /authorize endpoint

---
 src/server/auth/handlers/authorize.ts | 89 +++++++++++++++++++++++++++
 src/server/auth/handlers/register.ts  |  2 +-
 2 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 src/server/auth/handlers/authorize.ts

diff --git a/src/server/auth/handlers/authorize.ts b/src/server/auth/handlers/authorize.ts
new file mode 100644
index 00000000..1f29b0bb
--- /dev/null
+++ b/src/server/auth/handlers/authorize.ts
@@ -0,0 +1,89 @@
+import { RequestHandler } from "express";
+import { z } from "zod";
+import { OAuthRegisteredClientsStore } from "../clients.js";
+
+export type AuthorizationHandlerOptions = {
+  /**
+   * A store used to read information about registered OAuth clients.
+   */
+  store: OAuthRegisteredClientsStore;
+};
+
+const ClientAuthorizationParamsSchema = z.object({
+  client_id: z.string(),
+  redirect_uri: z.string().optional(),
+});
+
+const RequestAuthorizationParamsSchema = z.object({
+  response_type: z.literal("code"),
+  code_challenge: z.string(),
+  code_challenge_method: z.literal("S256"),
+  scope: z.string().optional(),
+  state: z.string().optional(),
+});
+
+export function authorizationHandler({ store }: AuthorizationHandlerOptions): RequestHandler {
+  return async (req, res) => {
+    if (req.method !== "GET" && req.method !== "POST") {
+      res.status(405).end("Method Not Allowed");
+      return;
+    }
+
+    let client_id, redirect_uri;
+    try {
+      ({ client_id, redirect_uri } = ClientAuthorizationParamsSchema.parse(req.query));
+    } catch (error) {
+      res.status(400).end(`Bad Request: ${error}`);
+      return;
+    }
+
+    const client = await store.getClient(client_id);
+    if (!client) {
+      res.status(400).end("Bad Request: invalid client_id");
+      return;
+    }
+
+    if (redirect_uri !== undefined) {
+      if (!client.redirect_uris.includes(redirect_uri)) {
+        res.status(400).end("Bad Request: invalid redirect_uri");
+        return;
+      }
+    } else if (client.redirect_uris.length === 1) {
+      redirect_uri = client.redirect_uris[0];
+    } else {
+      res.status(400).end("Bad Request: missing redirect_uri");
+      return;
+    }
+
+    let params;
+    try {
+      params = RequestAuthorizationParamsSchema.parse(req.query);
+    } catch (error) {
+      const errorUrl = new URL(redirect_uri);
+      errorUrl.searchParams.set("error", "invalid_request");
+      errorUrl.searchParams.set("error_description", String(error));
+      res.redirect(302, errorUrl.href);
+      return;
+    }
+
+    if (params.scope !== undefined && client.scope !== undefined) {
+      const requestedScopes = params.scope.split(" ");
+      const allowedScopes = new Set(client.scope.split(" "));
+
+      // If any requested scope is not in the client's registered scopes, error out
+      for (const scope of requestedScopes) {
+        if (!allowedScopes.has(scope)) {
+          const errorUrl = new URL(redirect_uri);
+          errorUrl.searchParams.set("error", "invalid_scope");
+          errorUrl.searchParams.set("error_description", `Client was not registered with scope ${scope}`);
+          res.redirect(302, errorUrl.href);
+          return;
+        }
+      }
+    }
+
+    // TODO: Store code challenge
+    // TODO: Generate authorization code
+    // TODO: Redirect to redirect_uri (handle in calling code)
+  };
+}
\ No newline at end of file
diff --git a/src/server/auth/handlers/register.ts b/src/server/auth/handlers/register.ts
index 32933316..bd5b080a 100644
--- a/src/server/auth/handlers/register.ts
+++ b/src/server/auth/handlers/register.ts
@@ -25,7 +25,7 @@ export function clientRegistrationHandler({ store, clientSecretExpirySeconds = D
     throw new Error("Client registration store does not support registering clients");
   }
 
-  // Nested router so we can configure middleware
+  // Nested router so we can configure middleware and restrict HTTP method
   const router = express.Router();
   router.use(express.json());