Token exchange body needs to be JSON

client/src/lib/auth.ts

@@ -66,9 +66,9 @@ export async function handleOAuthCallback(serverUrl: string, code: string): Prom
   const response = await fetch(metadata.token_endpoint, {
     method: 'POST',
     headers: {
-      'Content-Type': 'application/x-www-form-urlencoded',
+      'Content-Type': 'application/json',
     },
-    body: new URLSearchParams({
+    body: JSON.stringify({
       grant_type: 'authorization_code',
       code,
       code_verifier: codeVerifier,