Handle dynamic list of identity providers (#1800)

Author: robapaul88

auth/src/main/java/com/firebase/ui/auth/ui/idp/AuthMethodPickerActivity.java

@@ -51,7 +51,6 @@
 import com.google.firebase.auth.EmailAuthProvider;
 import com.google.firebase.auth.FacebookAuthProvider;
 import com.google.firebase.auth.FirebaseAuth;
-import com.google.firebase.auth.GithubAuthProvider;
 import com.google.firebase.auth.GoogleAuthProvider;
 import com.google.firebase.auth.PhoneAuthProvider;
 
@@ -229,14 +228,36 @@ private void populateIdpListCustomLayout(List<IdpConfig> providerConfigs) {
         for (IdpConfig idpConfig : providerConfigs) {
             final String providerId = providerOrEmailLinkProvider(idpConfig.getProviderId());
 
-            if (!providerButtonIds.containsKey(providerId)) {
+            Integer buttonResId = providerButtonIds.get(providerId);
+            if (buttonResId == null) {
                 throw new IllegalStateException("No button found for auth provider: " + idpConfig.getProviderId());
             }
 
-            @IdRes int buttonId = providerButtonIds.get(providerId);
+            @IdRes int buttonId = buttonResId;
             View loginButton = findViewById(buttonId);
             handleSignInOperation(idpConfig, loginButton);
         }
+        //hide custom layout buttons that don't have their identity provider set
+        for (String providerBtnId : providerButtonIds.keySet()) {
+            if (providerBtnId == null) {
+                continue;
+            }
+            boolean hasProvider = false;
+            for (IdpConfig idpConfig : providerConfigs) {
+                if (providerBtnId.equals(idpConfig.getProviderId())) {
+                    hasProvider = true;
+                    break;
+                }
+            }
+            if (!hasProvider) {
+                Integer resId = providerButtonIds.get(providerBtnId);
+                if (resId == null) {
+                    continue;
+                }
+                @IdRes int buttonId = resId;
+                findViewById(buttonId).setVisibility(View.GONE);
+            }
+        }
     }
 
     @NonNull