feat: Implement Apple Sign-In for Android by adding a callback function, updating redirect URI, and configuring the Android manifest.

functions/index.js

@@ -144,3 +144,22 @@ exports.onExpenseCreated = functions.firestore
             { groupId: groupId }
         );
     });
+
+exports.callbacks_signInWithApple = functions.https.onRequest((req, res) => {
+    const code = req.body.code;
+    const state = req.body.state;
+    const id_token = req.body.id_token;
+    const user = req.body.user;
+
+    const params = new URLSearchParams();
+    if (code) params.append('code', code);
+    if (state) params.append('state', state);
+    if (id_token) params.append('id_token', id_token);
+    if (user) params.append('user', user);
+
+    const qs = params.toString();
+    const packageName = 'be.devdayronvl.travel_mate';
+    const redirectUrl = `intent://callback?${qs}#Intent;package=${packageName};scheme=signinwithapple;end`;
+
+    res.redirect(302, redirectUrl);
+});