저장된 사용자 인증 정보로 사용자 로그인 처리

public class YourActivity extends AppCompatActivity {
  // ...

  private SignInClient oneTapClient;
  private BeginSignInRequest signInRequest;

  @Override
  public void onCreate(@Nullable Bundle savedInstanceState,
                       @Nullable PersistableBundle persistentState) {
      super.onCreate(savedInstanceState, persistentState);

      oneTapClient = Identity.getSignInClient(this);
      signInRequest = BeginSignInRequest.builder()
              .setPasswordRequestOptions(PasswordRequestOptions.builder()
                      .setSupported(true)
                      .build())
              .setGoogleIdTokenRequestOptions(GoogleIdTokenRequestOptions.builder()
                      .setSupported(true)
                      // Your server's client ID, not your Android client ID.
                      .setServerClientId(getString(R.string.default_web_client_id))
                      // Only show accounts previously used to sign in.
                      .setFilterByAuthorizedAccounts(true)
                      .build())
              // Automatically sign in when exactly one credential is retrieved.
              .setAutoSelectEnabled(true)
              .build();
      // ...
  }
  // ...
}

class YourActivity : AppCompatActivity() {
    // ...

    private lateinit var oneTapClient: SignInClient
    private lateinit var signInRequest: BeginSignInRequest

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        oneTapClient = Identity.getSignInClient(this)
        signInRequest = BeginSignInRequest.builder()
            .setPasswordRequestOptions(BeginSignInRequest.PasswordRequestOptions.builder()
                .setSupported(true)
                .build())
            .setGoogleIdTokenRequestOptions(
                BeginSignInRequest.GoogleIdTokenRequestOptions.builder()
                    .setSupported(true)
                    // Your server's client ID, not your Android client ID.
                    .setServerClientId(getString(R.string.your_web_client_id))
                    // Only show accounts previously used to sign in.
                    .setFilterByAuthorizedAccounts(true)
                    .build())
            // Automatically sign in when exactly one credential is retrieved.
            .setAutoSelectEnabled(true)
            .build()
        // ...
    }
    // ...
}

oneTapClient.beginSignIn(signUpRequest)
        .addOnSuccessListener(this, new OnSuccessListener<BeginSignInResult>() {
            @Override
            public void onSuccess(BeginSignInResult result) {
                try {
                    startIntentSenderForResult(
                            result.getPendingIntent().getIntentSender(), REQ_ONE_TAP,
                            null, 0, 0, 0);
                } catch (IntentSender.SendIntentException e) {
                    Log.e(TAG, "Couldn't start One Tap UI: " + e.getLocalizedMessage());
                }
            }
        })
        .addOnFailureListener(this, new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                // No saved credentials found. Launch the One Tap sign-up flow, or
                // do nothing and continue presenting the signed-out UI.
                Log.d(TAG, e.getLocalizedMessage());
            }
        });

oneTapClient.beginSignIn(signInRequest)
    .addOnSuccessListener(this) { result ->
        try {
            startIntentSenderForResult(
                result.pendingIntent.intentSender, REQ_ONE_TAP,
                null, 0, 0, 0, null)
        } catch (e: IntentSender.SendIntentException) {
            Log.e(TAG, "Couldn't start One Tap UI: ${e.localizedMessage}")
        }
    }
    .addOnFailureListener(this) { e ->
        // No saved credentials found. Launch the One Tap sign-up flow, or
        // do nothing and continue presenting the signed-out UI.
        Log.d(TAG, e.localizedMessage)
    }

public class YourActivity extends AppCompatActivity {

  // ...
  private static final int REQ_ONE_TAP = 2;  // Can be any integer unique to the Activity.
  private boolean showOneTapUI = true;
  // ...

  @Override
  protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
      super.onActivityResult(requestCode, resultCode, data);

      switch (requestCode) {
          case REQ_ONE_TAP:
              try {
                  SignInCredential credential = oneTapClient.getSignInCredentialFromIntent(data);
                  String idToken = credential.getGoogleIdToken();
                  String username = credential.getId();
                  String password = credential.getPassword();
                  if (idToken !=  null) {
                      // Got an ID token from Google. Use it to authenticate
                      // with your backend.
                      Log.d(TAG, "Got ID token.");
                  } else if (password != null) {
                      // Got a saved username and password. Use them to authenticate
                      // with your backend.
                      Log.d(TAG, "Got password.");
                  }
              } catch (ApiException e) {
                  // ...
              }
              break;
      }
  }
}

class YourActivity : AppCompatActivity() {

    // ...
    private val REQ_ONE_TAP = 2  // Can be any integer unique to the Activity
    private var showOneTapUI = true
    // ...

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)

        when (requestCode) {
             REQ_ONE_TAP -> {
                try {
                    val credential = oneTapClient.getSignInCredentialFromIntent(data)
                    val idToken = credential.googleIdToken
                    val username = credential.id
                    val password = credential.password
                    when {
                        idToken != null -> {
                            // Got an ID token from Google. Use it to authenticate
                            // with your backend.
                            Log.d(TAG, "Got ID token.")
                        }
                        password != null -> {
                            // Got a saved username and password. Use them to authenticate
                            // with your backend.
                            Log.d(TAG, "Got password.")
                        }
                        else -> {
                            // Shouldn't happen.
                            Log.d(TAG, "No ID token or password!")
                        }
                    }
                } catch (e: ApiException) {
                    // ...
                }
            }
        }
    }
    // ...
}

public class YourActivity extends AppCompatActivity {

  // ...
  private static final int REQ_ONE_TAP = 2;  // Can be any integer unique to the Activity.
  private boolean showOneTapUI = true;
  // ...

  @Override
  protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
      super.onActivityResult(requestCode, resultCode, data);

      switch (requestCode) {
          case REQ_ONE_TAP:
              try {
                  // ...
              } catch (ApiException e) {
                  switch (e.getStatusCode()) {
                      case CommonStatusCodes.CANCELED:
                          Log.d(TAG, "One-tap dialog was closed.");
                          // Don't re-prompt the user.
                          showOneTapUI = false;
                          break;
                      case CommonStatusCodes.NETWORK_ERROR:
                          Log.d(TAG, "One-tap encountered a network error.");
                          // Try again or just ignore.
                          break;
                      default:
                          Log.d(TAG, "Couldn't get credential from result."
                                  + e.getLocalizedMessage());
                          break;
                  }
              }
              break;
      }
  }
}

class YourActivity : AppCompatActivity() {

    // ...
    private val REQ_ONE_TAP = 2  // Can be any integer unique to the Activity
    private var showOneTapUI = true
    // ...

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)

        when (requestCode) {
            REQ_ONE_TAP -> {
                try {
                    // ...
                } catch (e: ApiException) {
                    when (e.statusCode) {
                        CommonStatusCodes.CANCELED -> {
                            Log.d(TAG, "One-tap dialog was closed.")
                            // Don't re-prompt the user.
                            showOneTapUI = false
                        }
                        CommonStatusCodes.NETWORK_ERROR -> {
                            Log.d(TAG, "One-tap encountered a network error.")
                            // Try again or just ignore.
                        }
                        else -> {
                            Log.d(TAG, "Couldn't get credential from result." +
                                " (${e.localizedMessage})")
                        }
                    }
                }
            }
        }
    }
    // ...
}