Cannot resolve symbol default_web_client_id in Firebase's Android Codelab
<p>I am trying to learn Firebase, so I went through the Android Codelab. The project they gave me however, had an error:</p>

<blockquote>
  <p>Cannot resolve symbol default_web_client_id</p>
</blockquote>

<p>And I didn't know how to solve it, since I didn't know the value of <code>default_web_client_id</code> or what it is. It is in the <code>onCreate()</code> method:
<strong>SigninActivity.java</strong></p>

<pre><code>@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_sign_in);
    mFirebaseAuth = FirebaseAuth.getInstance();

    // Assign fields
    mSignInButton = (SignInButton) findViewById(R.id.sign_in_button);

    // Set click listeners
    mSignInButton.setOnClickListener(this);

    // Configure Google Sign In
    GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(getString(R.string.default_web_client_id))
            .requestEmail()
            .build();
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
            .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
            .build();
}
</code></pre>

<p>I have no idea what it is, what's its value is, and why is it giving me this error. I haven't changed anything so far except for adding the <code>google-services.json</code>. I have added my <a href="http://en.wikipedia.org/wiki/SHA-1" rel="noreferrer">SHA-1</a> and enabled Google in the console.</p>