DataConnectAuth.kt: add a link to the docs to justify using the "sub" claim.

The unshortened URL is: https://firebase.google.com/docs/auth/admin/verify-id-tokens#verify_id_tokens_using_a_third-party_jwt_library

Here is what the page looked like when viewed on Oct 24, 2025:

https://github.com/user-attachments/assets/65f9d0ec-9067-40a7-a2d6-ce91e69d1dc4

diff --git a/firebase-dataconnect/src/main/kotlin/com/google/firebase/dataconnect/core/DataConnectAuth.kt b/firebase-dataconnect/src/main/kotlin/com/google/firebase/dataconnect/core/DataConnectAuth.kt
index e984150..55bb959 100644
--- a/firebase-dataconnect/src/main/kotlin/com/google/firebase/dataconnect/core/DataConnectAuth.kt
+++ b/firebase-dataconnect/src/main/kotlin/com/google/firebase/dataconnect/core/DataConnectAuth.kt
@@ -63,6 +63,8 @@ internal class DataConnectAuth(

   private companion object {

+    // The "sub" claim is documented to be "a non-empty string and must be the uid of the user or
+    // device". See http://goo.gle/4oGjEQt for the relevant Firebase documentation.
     fun com.google.firebase.auth.GetTokenResult.getAuthUid(): String? = claims["sub"] as? String
   }
 }

Author: dconeybe

firebase-dataconnect/src/main/kotlin/com/google/firebase/dataconnect/core/DataConnectAuth.kt

@@ -63,6 +63,8 @@ internal class DataConnectAuth(
 
   private companion object {
 
+    // The "sub" claim is documented to be "a non-empty string and must be the uid of the user or
+    // device". See http://goo.gle/4oGjEQt for the relevant Firebase documentation.
     fun com.google.firebase.auth.GetTokenResult.getAuthUid(): String? = claims["sub"] as? String
   }
 }