fix email link sign in button not shown when using custom layout

Author: rstjepanj

auth/src/main/java/com/firebase/ui/auth/AuthMethodPickerLayout.java

@@ -143,6 +143,14 @@ public AuthMethodPickerLayout.Builder setEmailButtonId(@IdRes int emailButton) {
             return this;
         }
 
+        /**
+         * Set the ID of the Email link sign in button in the custom layout.
+         */
+        public AuthMethodPickerLayout.Builder setEmailLinkButtonId(@IdRes int emailLinkButton) {
+            providersMapping.put(EmailAuthProvider.EMAIL_LINK_SIGN_IN_METHOD, emailLinkButton);
+            return this;
+        }
+
         /**
          * Set the ID of the Phone Number sign in button in the custom layout.
          */

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

@@ -224,9 +224,7 @@ private void populateIdpList(List<IdpConfig> providerConfigs) {
     private void populateIdpListCustomLayout(List<IdpConfig> providerConfigs) {
         Map<String, Integer> providerButtonIds = customLayout.getProvidersButton();
         for (IdpConfig idpConfig : providerConfigs) {
-            final String providerId = providerOrEmailLinkProvider(idpConfig.getProviderId());
-
-            Integer buttonResId = providerButtonIds.get(providerId);
+            Integer buttonResId = providerButtonIds.get(idpConfig.getProviderId());
             if (buttonResId == null) {
                 throw new IllegalStateException("No button found for auth provider: " + idpConfig.getProviderId());
             }
@@ -258,15 +256,6 @@ private void populateIdpListCustomLayout(List<IdpConfig> providerConfigs) {
         }
     }
 
-    @NonNull
-    private String providerOrEmailLinkProvider(@NonNull String providerId) {
-        if (providerId.equals(EmailAuthProvider.EMAIL_LINK_SIGN_IN_METHOD)) {
-            return EmailAuthProvider.PROVIDER_ID;
-        }
-
-        return providerId;
-    }
-
     private void handleSignInOperation(final IdpConfig idpConfig, View view) {
         ViewModelProvider supplier = new ViewModelProvider(this);
         final String providerId = idpConfig.getProviderId();

auth/src/test/java/com/firebase/ui/auth/ui/idp/AuthMethodPickerActivityTest.java

@@ -130,7 +130,7 @@ public void testCustomAuthMethodPickerLayoutWithEmailLink() {
 
         AuthMethodPickerLayout customLayout = new AuthMethodPickerLayout
                 .Builder(R.layout.fui_provider_button_email)
-                .setEmailButtonId(R.id.email_button)
+                .setEmailLinkButtonId(R.id.email_button)
                 .build();
 
         AuthMethodPickerActivity authMethodPickerActivity = createActivityWithCustomLayout(providers, customLayout, false);