diff --git a/auth/src/main/java/com/firebase/ui/auth/AuthUI.java b/auth/src/main/java/com/firebase/ui/auth/AuthUI.java
index 465e3e5ad..a17567c1a 100644
--- a/auth/src/main/java/com/firebase/ui/auth/AuthUI.java
+++ b/auth/src/main/java/com/firebase/ui/auth/AuthUI.java
@@ -22,6 +22,7 @@
 import android.support.annotation.DrawableRes;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.support.annotation.StringDef;
 import android.support.annotation.StyleRes;
 import android.support.v4.app.FragmentActivity;
 
@@ -73,6 +74,13 @@
  * for examples on how to get started with FirebaseUI Auth.
  */
 public class AuthUI {
+    @StringDef({
+                       EmailAuthProvider.PROVIDER_ID, EMAIL_PROVIDER,
+                       GoogleAuthProvider.PROVIDER_ID, GOOGLE_PROVIDER,
+                       FacebookAuthProvider.PROVIDER_ID, FACEBOOK_PROVIDER,
+                       TwitterAuthProvider.PROVIDER_ID, TWITTER_PROVIDER
+               })
+    public @interface SupportedProvider {}
 
     /**
      * Provider identifier for email and password credentials, for use with
@@ -333,7 +341,7 @@ public static class IdpConfig implements Parcelable {
         private final String mProviderId;
         private final List<String> mScopes;
 
-        private IdpConfig(@NonNull String providerId, List<String> scopes) {
+        private IdpConfig(@SupportedProvider @NonNull String providerId, List<String> scopes) {
             mProviderId = providerId;
             mScopes = Collections.unmodifiableList(scopes);
         }
@@ -343,6 +351,7 @@ private IdpConfig(Parcel in) {
             mScopes = Collections.unmodifiableList(in.createStringArrayList());
         }
 
+        @SupportedProvider
         public String getProviderId() {
             return mProviderId;
         }
@@ -398,7 +407,7 @@ public String toString() {
         }
 
         public static class Builder {
-            private String mProviderId;
+            @SupportedProvider private String mProviderId;
             private List<String> mScopes = new ArrayList<>();
 
             /**
@@ -408,7 +417,7 @@ public static class Builder {
              *                   AuthUI#GOOGLE_PROVIDER}. See {@link AuthUI#SUPPORTED_PROVIDERS} for
              *                   the complete list of supported Identity providers
              */
-            public Builder(@NonNull String providerId) {
+            public Builder(@SupportedProvider @NonNull String providerId) {
                 if (!SUPPORTED_PROVIDERS.contains(providerId)) {
                     throw new IllegalArgumentException("Unkown provider: " + providerId);
                 }
diff --git a/auth/src/main/java/com/firebase/ui/auth/IdpResponse.java b/auth/src/main/java/com/firebase/ui/auth/IdpResponse.java
index dabdd078e..b83b2fbbc 100644
--- a/auth/src/main/java/com/firebase/ui/auth/IdpResponse.java
+++ b/auth/src/main/java/com/firebase/ui/auth/IdpResponse.java
@@ -84,6 +84,7 @@ public Intent toIntent() {
      * Get the type of provider. e.g. {@link AuthUI#GOOGLE_PROVIDER}
      */
     @NonNull
+    @AuthUI.SupportedProvider
     public String getProviderType() {
         return mProviderId;
     }
@@ -158,7 +159,7 @@ public static class Builder {
         private String mToken;
         private String mSecret;
 
-        public Builder(@NonNull String providerId, @Nullable String email) {
+        public Builder(@AuthUI.SupportedProvider @NonNull String providerId, @Nullable String email) {
             mProviderId = providerId;
             mEmail = email;
         }
diff --git a/auth/src/main/java/com/firebase/ui/auth/provider/FacebookProvider.java b/auth/src/main/java/com/firebase/ui/auth/provider/FacebookProvider.java
index 033ae151a..c8de93d7d 100644
--- a/auth/src/main/java/com/firebase/ui/auth/provider/FacebookProvider.java
+++ b/auth/src/main/java/com/firebase/ui/auth/provider/FacebookProvider.java
@@ -89,6 +89,7 @@ public String getName(Context context) {
     }
 
     @Override
+    @AuthUI.SupportedProvider
     public String getProviderId() {
         return FacebookAuthProvider.PROVIDER_ID;
     }
diff --git a/auth/src/main/java/com/firebase/ui/auth/provider/GoogleProvider.java b/auth/src/main/java/com/firebase/ui/auth/provider/GoogleProvider.java
index 27370f404..2b978ac1b 100644
--- a/auth/src/main/java/com/firebase/ui/auth/provider/GoogleProvider.java
+++ b/auth/src/main/java/com/firebase/ui/auth/provider/GoogleProvider.java
@@ -26,6 +26,7 @@
 import android.util.Log;
 import android.widget.Toast;
 
+import com.firebase.ui.auth.AuthUI;
 import com.firebase.ui.auth.AuthUI.IdpConfig;
 import com.firebase.ui.auth.IdpResponse;
 import com.firebase.ui.auth.R;
@@ -104,6 +105,7 @@ public String getName(Context context) {
     }
 
     @Override
+    @AuthUI.SupportedProvider
     public String getProviderId() {
         return GoogleAuthProvider.PROVIDER_ID;
     }
diff --git a/auth/src/main/java/com/firebase/ui/auth/provider/TwitterProvider.java b/auth/src/main/java/com/firebase/ui/auth/provider/TwitterProvider.java
index 34e3485c2..f8d70e6bb 100644
--- a/auth/src/main/java/com/firebase/ui/auth/provider/TwitterProvider.java
+++ b/auth/src/main/java/com/firebase/ui/auth/provider/TwitterProvider.java
@@ -7,6 +7,7 @@
 import android.support.annotation.LayoutRes;
 import android.util.Log;
 
+import com.firebase.ui.auth.AuthUI;
 import com.firebase.ui.auth.IdpResponse;
 import com.firebase.ui.auth.R;
 import com.google.firebase.auth.AuthCredential;
@@ -54,6 +55,7 @@ public String getName(Context context) {
     }
 
     @Override
+    @AuthUI.SupportedProvider
     public String getProviderId() {
         return TwitterAuthProvider.PROVIDER_ID;
     }
diff --git a/auth/src/main/java/com/firebase/ui/auth/ui/User.java b/auth/src/main/java/com/firebase/ui/auth/ui/User.java
index e6843b896..7fab9ace1 100644
--- a/auth/src/main/java/com/firebase/ui/auth/ui/User.java
+++ b/auth/src/main/java/com/firebase/ui/auth/ui/User.java
@@ -9,6 +9,8 @@
 import android.support.annotation.Nullable;
 import android.support.annotation.RestrictTo;
 
+import com.firebase.ui.auth.AuthUI;
+
 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
 public class User implements Parcelable {
     public static final Parcelable.Creator<User> CREATOR = new Parcelable.Creator<User>() {
@@ -57,6 +59,7 @@ public String getName() {
     }
 
     @Nullable
+    @AuthUI.SupportedProvider
     public String getProvider() {
         return mProvider;
     }
@@ -94,7 +97,7 @@ public Builder setName(String name) {
             return this;
         }
 
-        public Builder setProvider(String provider) {
+        public Builder setProvider(@AuthUI.SupportedProvider String provider) {
             mProvider = provider;
             return this;
         }
diff --git a/auth/src/main/java/com/firebase/ui/auth/ui/idp/CredentialSignInHandler.java b/auth/src/main/java/com/firebase/ui/auth/ui/idp/CredentialSignInHandler.java
index aa620c53c..9f7cba4f3 100644
--- a/auth/src/main/java/com/firebase/ui/auth/ui/idp/CredentialSignInHandler.java
+++ b/auth/src/main/java/com/firebase/ui/auth/ui/idp/CredentialSignInHandler.java
@@ -20,6 +20,7 @@
 import android.support.annotation.RestrictTo;
 import android.util.Log;
 
+import com.firebase.ui.auth.AuthUI;
 import com.firebase.ui.auth.ErrorCodes;
 import com.firebase.ui.auth.IdpResponse;
 import com.firebase.ui.auth.ResultCodes;
diff --git a/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SignInDelegate.java b/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SignInDelegate.java
index 2632bc7ec..a4d19aaa4 100644
--- a/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SignInDelegate.java
+++ b/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SignInDelegate.java
@@ -11,6 +11,7 @@
 import android.support.v4.app.FragmentManager;
 import android.text.TextUtils;
 import android.util.Log;
+
 import com.firebase.ui.auth.AuthUI;
 import com.firebase.ui.auth.AuthUI.IdpConfig;
 import com.firebase.ui.auth.IdpResponse;
@@ -194,7 +195,7 @@ public void onActivityResult(int requestCode, int resultCode, Intent data) {
     private List<String> getSupportedAccountTypes() {
         List<String> accounts = new ArrayList<>();
         for (AuthUI.IdpConfig idpConfig : mHelper.getFlowParams().providerInfo) {
-            String providerId = idpConfig.getProviderId();
+            @AuthUI.SupportedProvider String providerId = idpConfig.getProviderId();
             if (providerId.equals(GoogleAuthProvider.PROVIDER_ID)
                     || providerId.equals(FacebookAuthProvider.PROVIDER_ID)
                     || providerId.equals(TwitterAuthProvider.PROVIDER_ID)) {
diff --git a/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SmartLockBase.java b/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SmartLockBase.java
index 9f410d7fc..3deeee234 100644
--- a/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SmartLockBase.java
+++ b/auth/src/main/java/com/firebase/ui/auth/util/signincontainer/SmartLockBase.java
@@ -9,6 +9,7 @@
 import android.util.Pair;
 import android.widget.Toast;
 
+import com.firebase.ui.auth.AuthUI;
 import com.firebase.ui.auth.ui.FragmentBase;
 import com.google.android.gms.auth.api.credentials.Credential;
 import com.google.android.gms.auth.api.credentials.IdentityProviders;
@@ -42,7 +43,7 @@ public abstract class SmartLockBase<R extends Result> extends FragmentBase imple
      * Translate a Firebase Auth provider ID (such as {@link GoogleAuthProvider#PROVIDER_ID}) to
      * a Credentials API account type (such as {@link IdentityProviders#GOOGLE}).
      */
-    public static String providerIdToAccountType(@NonNull String providerId) {
+    public static String providerIdToAccountType(@AuthUI.SupportedProvider @NonNull String providerId) {
         switch (providerId) {
             case GoogleAuthProvider.PROVIDER_ID:
                 return IdentityProviders.GOOGLE;
@@ -58,6 +59,7 @@ public static String providerIdToAccountType(@NonNull String providerId) {
         }
     }
 
+    @AuthUI.SupportedProvider
     public static String accountTypeToProviderId(@NonNull String accountType) {
         switch (accountType) {
             case IdentityProviders.GOOGLE:
@@ -84,7 +86,7 @@ public static List<Credential> credentialsFromFirebaseUser(@NonNull FirebaseUser
         List<Credential> credentials = new ArrayList<>();
         for (UserInfo userInfo : user.getProviderData()) {
             // Get provider ID from Firebase Auth
-            String providerId = userInfo.getProviderId();
+            @AuthUI.SupportedProvider String providerId = userInfo.getProviderId();
 
             // Convert to Credentials API account type
             String accountType = providerIdToAccountType(providerId);
@@ -132,10 +134,6 @@ public void onStop() {
     @Override
     public void onDestroy() {
         super.onDestroy();
-        cleanup();
-    }
-
-    public void cleanup() {
         if (mGoogleApiClient != null) {
             mGoogleApiClient.disconnect();
         }