diff --git a/packages/dart_firebase_admin/lib/src/auth/token_verifier.dart b/packages/dart_firebase_admin/lib/src/auth/token_verifier.dart
index e65f78a..8a065f1 100644
--- a/packages/dart_firebase_admin/lib/src/auth/token_verifier.dart
+++ b/packages/dart_firebase_admin/lib/src/auth/token_verifier.dart
@@ -300,11 +300,12 @@ class DecodedIdToken {
     required this.phoneNumber,
     required this.picture,
     required this.sub,
-    required this.uid,
+    this.uid,
   });
 
   @internal
   factory DecodedIdToken.fromMap(Map<String, Object?> map) {
+    final firebaseMap = Map<String, Object?>.from(map['firebase']! as Map);
     return DecodedIdToken(
       aud: map['aud']! as String,
       authTime: DateTime.fromMillisecondsSinceEpoch(
@@ -314,18 +315,19 @@ class DecodedIdToken {
       emailVerified: map['email_verified'] as bool?,
       exp: map['exp']! as int,
       firebase: TokenProvider(
-        identities: Map.from(map['firebase']! as Map),
-        signInProvider: map['sign_in_provider']! as String,
-        signInSecondFactor: map['sign_in_second_factor'] as String?,
-        secondFactorIdentifier: map['second_factor_identifier'] as String?,
-        tenant: map['tenant'] as String?,
+        identities: firebaseMap,
+        signInProvider: firebaseMap['sign_in_provider']! as String,
+        signInSecondFactor: firebaseMap['sign_in_second_factor'] as String?,
+        secondFactorIdentifier:
+            firebaseMap['second_factor_identifier'] as String?,
+        tenant: firebaseMap['tenant'] as String?,
       ),
       iat: map['iat']! as int,
       iss: map['iss']! as String,
       phoneNumber: map['phone_number'] as String?,
       picture: map['picture'] as String?,
       sub: map['sub']! as String,
-      uid: map['uid']! as String,
+      uid: map['uid'] != null ? map['uid']! as String : null,
     );
   }
 
@@ -398,7 +400,7 @@ class DecodedIdToken {
   ///
   /// This value is not actually in the JWT token claims itself. It is added as a
   /// convenience, and is set as the value of the [`sub`](#sub) property.
-  String uid;
+  String? uid;
 
   /**
    * Other arbitrary claims included in the ID token.
diff --git a/packages/dart_firebase_admin/lib/src/utils/jwt.dart b/packages/dart_firebase_admin/lib/src/utils/jwt.dart
index ce546cf..9bc2a21 100644
--- a/packages/dart_firebase_admin/lib/src/utils/jwt.dart
+++ b/packages/dart_firebase_admin/lib/src/utils/jwt.dart
@@ -96,9 +96,40 @@ class PublicKeySignatureVerifier implements SignatureVerifier {
   final KeyFetcher keyFetcher;
 
   @override
-  Future<bool> verify(String token) {
-    throw UnimplementedError();
-    // verifyJwtSignature(token);
+  Future<void> verify(String token) async {
+    try {
+      final jwt = JWT.decode(token);
+      final kid = jwt.header?['kid'] as String?;
+
+      if (kid == null) {
+        throw JwtError(
+          JwtErrorCode.noKidInHeader,
+          'no-kid-in-header-error',
+        );
+      }
+
+      final publicKeys = await keyFetcher.fetchPublicKeys();
+      final publicKey = publicKeys[kid];
+
+      if (publicKey == null) {
+        throw JwtError(
+          JwtErrorCode.noMatchingKid,
+          'no-matching-kid-error',
+        );
+      }
+      JWT.verify(
+        token,
+        RSAPublicKey.cert(publicKey),
+      );
+    } on JWTExpiredException {
+      throw JwtError(
+        JwtErrorCode.tokenExpired,
+        'The provided token has expired. Get a fresh token from your client app and try again.',
+      );
+    } on JWTException catch (e) {
+      // TODO: Handle specific JWTException types to provide detailed error messages.
+      throw JwtError(JwtErrorCode.unknown, e.message);
+    }
   }
 }
 
@@ -160,7 +191,8 @@ enum JwtErrorCode {
   invalidSignature('invalid-token'),
   noMatchingKid('no-matching-kid-error'),
   noKidInHeader('no-kid-error'),
-  keyFetchError('key-fetch-error');
+  keyFetchError('key-fetch-error'),
+  unknown('unknown');
 
   const JwtErrorCode(this.value);