JJWT libary to generate token for authentication with Firebase on Android

Question

I am trying to implement Linkedin Signin and then authenticate with Firebase. The only way to do so, since Linkedin is not in the current Firebase simple login providers is to:

1. Login with Linkedin, grant the token as shown here.
2. Get the Id of the Linkedin user.
3. Make a token just like Firebase indicates.
4. In order to signInWithCustomToken just like it indicates here, following then the procedure over here:

   Create custom tokens using a third-party JWT library

Now, I have done all these. Here is the generating token code with JJWT library:

long nowSeconds = System.currentTimeMillis()/1000;
        Date current_date = new Date(nowSeconds);
        KeyPair myKey = RsaProvider.generateKeyPair();
        long expMillis = nowSeconds + 3000;
        Date exp_time = new Date(expMillis);
        String compactJws = Jwts.builder()
                .setSubject(ACCOUNT_EMAIL)
                .setIssuer(ACCOUNT_EMAIL)
                .setAudience("https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit")
                .setIssuedAt(current_date)
                .setExpiration(exp_time)
                .setId(linkedinId)
                .signWith(SignatureAlgorithm.RS256, myKey.getPrivate())
                .compact();

but I have incorrect Token format because:

iat Issued-at time The current time, in seconds since the UNIX epoch

exp Expiration time The time, in seconds since the UNIX epoch, at which the token expires. It can be a maximum of 3600 seconds later than the iat. Note: this only controls the time when the custom token itself expires. But once you sign a user in using signInWithCustomToken(), they will remain signed in into the device until their session is invalidated or the user signs out.

Because Firebase wants seconds and not Date. I can't pass a long value on setIssuedAt or setExpiration, as a Date Object is needed as a parameter.

So, how can I put a long value (the seconds) there? UPDATE: I have found a way to pass the timestamp like this:

long nowSeconds = System.currentTimeMillis()/1000;
        Date current_date = new Date(nowSeconds);
        KeyPair myKey = RsaProvider.generateKeyPair();
        long expSeconds = nowSeconds + 3000;
        Date exp_time = new Date(expSeconds);
        String compactJws = Jwts.builder()
                .setSubject(ACCOUNT_EMAIL)
                .setIssuer(ACCOUNT_EMAIL)
                .setAudience("https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit")
                .claim("iat",current_date.getTime())
                .claim("exp",exp_time.getTime())
                .claim("uid",uid)
                .signWith(SignatureAlgorithm.RS256,myKey.getPrivate())
                .compact();

But still my Token format is incorrect:

 E/AndroidRuntime: FATAL EXCEPTION: main
                                                                          Process: com.example.qrcodereader, PID: 24239


com.google.android.gms.tasks.RuntimeExecutionException: com.google.firebase.auth.FirebaseAuthInvalidCredentialsException: The custom token format is incorrect. Please check the documentation.
                                                                          at com.google.android.gms.tasks.zzh.getResult(Unknown Source)
                                                                          at com.example.qrcodereader.LoginActivity$6.onComplete(LoginActivity.java:268)
                                                                          at com.google.android.gms.tasks.zzc$1.run(Unknown Source)
                                                                          at android.os.Handler.handleCallback(Handler.java:739)
                                                                          at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                          at android.os.Looper.loop(Looper.java:148)
                                                                          at android.app.ActivityThread.main(ActivityThread.java:7325)
                                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
                                                                       Caused by: com.google.firebase.auth.FirebaseAuthInvalidCredentialsException: The custom token format is incorrect. Please check the documentation.
                                                                          at com.google.android.gms.internal.zzbix.zzcb(Unknown Source)
                                                                          at com.google.android.gms.internal.zzbiu$zzj.zza(Unknown Source)
                                                                          at com.google.android.gms.internal.zzbjf.zzcc(Unknown Source)
                                                                          at com.google.android.gms.internal.zzbjf$zza.onFailure(Unknown Source)
                                                                          at com.google.android.gms.internal.zzbja$zza.onTransact(Unknown Source)
                                                                          at android.os.Binder.execTransact(Binder.java:453)

Does anyone know what's the mistake here? I really can't figure it out.

Answer 1

A Date con not be built with seconds. It needs a milliseconds value. This code is incorrect.

Date current_date = new Date(nowSeconds);

Use the following code

KeyPair myKey = RsaProvider.generateKeyPair();
Date current_date = new Date();
Calendar calendar = Calendar.getInstance(); 
calendar.add(Calendar.SECOND, 3000);
Date exp_time = calendar.getTime();
String compactJws = Jwts.builder()
        .setSubject(ACCOUNT_EMAIL)
        .setIssuer(ACCOUNT_EMAIL)
        .setAudience("https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit")
        .setIssuedAt(current_date)
        .setExpiration(exp_time)
        .setId(linkedinId)
        .signWith(SignatureAlgorithm.RS256, myKey.getPrivate())
        .compact();

If you want to use the second way .claim() the divide the values by 1000 to get seconds

.claim("exp",exp_time.getTime()/1000)