title: Android BiometricPrompt.Builder.authenticate() not showing any dialog
body: <p>This is my code to show the prompt for fingerprint authentication in Android P:</p>
  
  <pre><code>private void displayBiometricPrompt() {
      DialogInterface.OnClickListener onClickListener = new DialogInterface.OnClickListener() {
          @Override
          public void onClick(DialogInterface dialog, int which) {
              Toast.makeText(getApplicationContext(), "Fingerprint Authentication cancelled", Toast.LENGTH_LONG);
          }
      };
      BiometricPrompt bm = new BiometricPrompt.Builder(getApplicationContext())
              .setTitle("Add a title")
              .setSubtitle("Add a subtitle")
              .setDescription("Add a description")
              .setNegativeButton("CANCEL", getMainExecutor(), onClickListener)
              .build();
              bm.authenticate(getCancellationSignal(), getMainExecutor(), getAuthenticationCallback());
  }
  </code></pre>
  
  <p>Unfortunately it is not working, since it's not displaying any dialog or prompt for fingerprint authorization. </p>
  
  <p>There is also no error in my code, I do not get any exceptions.</p>
  
  <p>I checked the permissions and everything seems to be as required for the biometric prompt.</p>
  
  <p>There is just nothing happening.</p>
  
  <p>Can anyone help me in finding out how?</p>
  
  <p>Appreciate any Help</p>