Sign-In Authentication Using Phone Number

Phone number authentication is the last sign-in method, which we will discuss in the authentication section. Many organizations widely used these authentication method.

We can use Firebase authentication to the sign-in user by sending a text message to the user's phone.

The user will sign-in using a one-time code that they have received in their message box.

We will go through the whole flow that how we can verify it and write all the code for that. For sign-in authentication using the phone number, we can also use the Firebase UI, which we have discussed earlier.

Starting steps are the same, such as creating a Firebase project, creating an Android Studio project, adding firebase to our Android app, adding firebase-auth and firebase-core dependencies, adding SHA-1 and SHA-256 keys, add JSON file, and apply plugins. The next steps are to enable phone number authentication in Firebase console. After these preliminary steps, we have to perform the following steps:

Step1:

Now, we will add permission to use the Internet in our Manifest file.

Step2:

Now, we will modify our 'activity_main.xml' file for phone number authentication. The layout design will be as followed:

Sign-In Authentication Using Phone Number

Step3:

Now, we will code for the phone number authentication. We will modify our 'MainActivity.java' file. Below is the code for the phone number authentication.

//Implementing onClickListener
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    
    private static final String TAG = "PhoneAuthActivity";

    //Adding a member variable for the key verification in progress
    private static final String KEY_VERIFY_IN_PROGRESS = "key_verify_in_progress";

    //Creating FirebaseAuth member variable
    private FirebaseAuth mAuth;

    //Adding a bunch of member variables for view groups, edit text, and buttons.
    private ViewGroup mPhoneNumberViews;
    private ViewGroup mSignedInViews;

    private EditText mPhoneNumberField;
    private EditText mVerificationField;

    private Button mStartButton;
    private Button mVerifyButton;
    private Button mResendButton;
    private Button mSignOutButton;
    
    //Setting Boolean to say whether or not we are in progress. 
    private boolean mVerificationInProgress = false;

    //Adding verification id as a member variable. 
    private String mVerificationId;
    
    //Adding a member variable for PhoneAuthProvider.ForceResendingToken callback. 
    private PhoneAuthProvider.ForceResendingToken mResendToken;
    
    //Adding a member variable for a callback which is our PhoneAuthProvider.OnVerificationStateChangeCallbacks.
    private PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallbacks;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        // Restoring the instance state
        if (savedInstanceState != null) {
            onRestoreInstanceState(savedInstanceState);
        }

        // Assigning all the views
        mPhoneNumberViews = findViewById(R.id.phoneAuthFields);
        mSignedInViews = findViewById(R.id.signedInButtons);

        mPhoneNumberField = findViewById(R.id.fieldPhoneNumber);
        mVerificationField = findViewById(R.id.fieldVerificationCode);

        mStartButton = findViewById(R.id.buttonStartVerification);
        mVerifyButton = findViewById(R.id.buttonVerifyPhone);
        mResendButton = findViewById(R.id.buttonResend);
        mSignOutButton = findViewById(R.id.signOutButton);

        // Setting all the click listeners
        mStartButton.setOnClickListener(this);
        mVerifyButton.setOnClickListener(this);
        mResendButton.setOnClickListener(this);
        mSignOutButton.setOnClickListener(this);


        // Initialize Firebase Auth
        mAuth = FirebaseAuth.getInstance();

        // Initializing phone auth callbacks  (For verification, Not entering code yet, To get text send to device)
        mCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {

            @Override
            public void onVerificationCompleted(PhoneAuthCredential credential) {
                // It will be invoked in two situations, i.e., instant verification and auto-retrieval:
               // 1 - In few of the cases, the phone number can be instantly verified without needing to  enter or send a verification code.
              // 2 - On some devices, Google Play services can automatically detect the incoming verification SMS and perform verification without
              //     user action.
                Log.d(TAG, "onVerificationCompleted:" + credential);
                mVerificationInProgress = false;

                //Calling signInWithPhoneAuthCredential.
                signInWithPhoneAuthCredential(credential);
            }

            //Creating onVerificationFailed() method.
            @Override
            public void onVerificationFailed(FirebaseException e) {
                // It is invoked when an invalid request is made for verification.                 //For instance, if the phone number format is not valid.
                Log.w(TAG, "onVerificationFailed", e);
                mVerificationInProgress = false;

                if (e instanceof FirebaseAuthInvalidCredentialsException) {
                    // Invalid request
                    // Setting error to text field
                    mPhoneNumberField.setError("Invalid phone number.");
                } else if (e instanceof FirebaseTooManyRequestsException) {
                    // The SMS quota has been exceeded for the project                     Toast.makeText(getApplicationContext(), "Quota exceeded", Toast.LENGTH_SHORT).show();
                }
            }
             // Creating onCodeSent() method called after the verification code has been sent by SMS to the provided phone number.   
            @Override
            public void onCodeSent(String verificationId,
                                   PhoneAuthProvider.ForceResendingToken token) {
                 // The SMS verification code will be sent to the provided phone number
                // Now need to ask the user for entering the code and then construct a credential
                // through integrating the code with a verification ID.
                Log.d(TAG, "onCodeSent:" + verificationId);

                // Save the verification ID and resend token to use them later
                mVerificationId = verificationId;
                mResendToken = token;
            }
        };
    }
    // Creating onStart method.
    @Override
    public void onStart() {
        super.onStart();

        // Checking if the user is signed in or not. If signed in, then update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();

        if (currentUser != null) {
            Log.d(TAG, "Currently Signed in: " + currentUser.getEmail());
            Toast.makeText(MainActivity.this, "Currently Logged in: " + currentUser.getEmail(), Toast.LENGTH_LONG).show();
            mPhoneNumberViews.setVisibility(View.GONE);
            mSignedInViews.setVisibility(View.VISIBLE);
        }
        else {
            mPhoneNumberViews.setVisibility(View.VISIBLE);
            mSignedInViews.setVisibility(View.GONE);
        }

        //check if a verification is in progress. If it is then we have to re verify.
        if (mVerificationInProgress && validatePhoneNumber()) {
            startPhoneNumberVerification(mPhoneNumberField.getText().toString());
        }
    }
    //Implementing SaveInstanceState to save the flag.
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBoolean(KEY_VERIFY_IN_PROGRESS, mVerificationInProgress);
    }

    //Implementing RestoreInstanceState to restore the flag.
    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        mVerificationInProgress = savedInstanceState.getBoolean(KEY_VERIFY_IN_PROGRESS);
    }

    // Creating startPhoneNumberVerification() method
   //Getting text code sent. So we can use it to sign-in.    
   private void startPhoneNumberVerification(String phoneNumber) {
        PhoneAuthProvider.getInstance().verifyPhoneNumber(
                phoneNumber,        // Phone number to verify
                60,                 // Timeout duration
                TimeUnit.SECONDS,   // Unit of timeout
                this,               // Activity (for callback binding)
                mCallbacks);        // OnVerificationStateChangedCallbacks

        //Setting flag to say that the verification is in process.
        mVerificationInProgress = true;
    }

     //Creating a helper method for verification of phone number with code.
    // Entering code and manually signing in with that code
    private void verifyPhoneNumberWithCode(String verificationId, String code) {
        PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationId, code);
        signInWithPhoneAuthCredential(credential);
    }

    // Creating helper method signInWithPhoneAuthCredential(). 
    //Use text to sign-in. 
    private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) {
        
         //Adding onCompleteListener to signInWithCredential.  
         mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            //Sign-In is successful, update the UI with the signed-in user's information
                            Log.d(TAG, "signInWithCredential:success");
                            FirebaseUser user = task.getResult().getUser();
                            mPhoneNumberViews.setVisibility(View.GONE);
                            mSignedInViews.setVisibility(View.VISIBLE);
                        } else {
                            // If the Sign-In fails, it will display a message and also update the UI                              
                            Log.w(TAG, "signInWithCredential:failure", task.getException());
                            if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                                // The verification code entered was invalid
                                mVerificationField.setError("Invalid code.");
                            }
                        }
                    }
                });
    }
    // Creating helper method for validating phone number. 
    private boolean validatePhoneNumber() {
        String phoneNumber = mPhoneNumberField.getText().toString();
        if (TextUtils.isEmpty(phoneNumber)) {
            mPhoneNumberField.setError("Invalid phone number.");
            return false;
        }

        return true;
    }
    
    //Creating helper method for resending verification code. 
    private void resendVerificationCode(String phoneNumber,
                                        PhoneAuthProvider.ForceResendingToken token) {
        PhoneAuthProvider.getInstance().verifyPhoneNumber(
                phoneNumber,        // Phone number to verify
                60,                 // Timeout duration
                TimeUnit.SECONDS,   // Unit of timeout
                this,               // Activity (for callback binding)
                mCallbacks,         // OnVerificationStateChangedCallbacks
                token);             // ForceResendingToken from callbacks
    }
    //Adding onClick method which handles the button clicks.
    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.buttonStartVerification:
                if (!validatePhoneNumber()) {
                    return;
                }
                //Calling startPhoneNumberVerification helper method for verifying phone number.
                startPhoneNumberVerification(mPhoneNumberField.getText().toString());
                break;
            case R.id.buttonVerifyPhone:
                String code = mVerificationField.getText().toString();
                if (TextUtils.isEmpty(code)) {
                    mVerificationField.setError("Cannot be empty.");
                    return;
                }
                //Call the verifyPhoneNumberWithCode () method.
                verifyPhoneNumberWithCode(mVerificationId, code);
                break;
            case R.id.buttonResend:
                //Call the resendVerificationCode () method.
                resendVerificationCode(mPhoneNumberField.getText().toString(), mResendToken);
                break;
            case R.id.signOutButton:
                //Call the signOut() method.
                signOut();
                break;
        }
    }
    //Create the signOut() method. 
    private void signOut() {
        mAuth.signOut();
        mPhoneNumberViews.setVisibility(View.VISIBLE);
        mSignedInViews.setVisibility(View.GONE);
    }
}

Output: