ユーザーの認証情報を保存する

Credential credential = new Credential.Builder(email)
        .setPassword(password)  // Important: only store passwords in this field.
                                // Android autofill uses this value to complete
                                // sign-in forms, so repurposing this field will
                                // likely cause errors.
        .build();

GoogleSignInAccount gsa = signInTask.getResult();
Credential credential = new Credential.Builder(gsa.getEmail())
        .setAccountType(IdentityProviders.GOOGLE)
        .setName(gsa.getDisplayName())
        .setProfilePictureUri(gsa.getPhotoUrl())
        .build();

mCredentialsClient.save(credential).addOnCompleteListener(
        new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    Log.d(TAG, "SAVE: OK");
                    Toast.makeText(activity, "Credentials saved", Toast.LENGTH_SHORT).show();
                    return;
                }

                Exception e = task.getException();
                if (e instanceof ResolvableApiException) {
                    // Try to resolve the save request. This will prompt the user if
                    // the credential is new.
                    ResolvableApiException rae = (ResolvableApiException) e;
                    try {
                        rae.startResolutionForResult(this, RC_SAVE);
                    } catch (IntentSender.SendIntentException exception) {
                        // Could not resolve the request
                        Log.e(TAG, "Failed to send resolution.", exception);
                        Toast.makeText(activity, "Save failed", Toast.LENGTH_SHORT).show();
                    }
                } else {
                    // Request has no resolution
                    Toast.makeText(activity, "Save failed", Toast.LENGTH_SHORT).show();
                }
            }
        });</pre>

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

        // ...

        if (requestCode == RC_SAVE) {
            if (resultCode == RESULT_OK) {
                Log.d(TAG, "SAVE: OK");
                Toast.makeText(this, "Credentials saved", Toast.LENGTH_SHORT).show();
            } else {
                Log.e(TAG, "SAVE: Canceled by user");
            }
        }

        // ...

    }