Passing State in Email Actions

You can pass state via a continue URL when sending email actions for password resets or verifying a user's email. This provides the user the ability to go back to the app after the action is completed. In addition, you can specify whether to handle the email action link directly from a mobile application when it is installed instead of a web page.

This can be extremely useful in the following common scenarios:

• A user, not currently logged in, may be trying to access content that requires the user to be signed in. However, the user might have forgotten their password and therefore trigger the reset password flow. At the end of the flow, the user expects to go back to the section of the app they were trying to access.

• An application may only offer access to verified accounts. For example, a newsletter may require the user to verify their email before subscribing. The user would go through the email verification flow and expect to go back to the app to complete their subscription.

• In other cases, the user may have started the flow from their mobile device and expect after verification to return back to their mobile app instead of the browser.

Having the ability to pass state via a continue URL is a powerful feature that Firebase Auth provides and which can significantly enhance the user experience.

Passing state of a continue URL in email actions

In order to securely pass a continue URL, the domain for the URL will need to be whitelisted in the Firebase console. This is done in the Authentication section by adding this domain to the list of Authorized domains under the Sign-in method tab if it is not already there.

An ActionCodeSettings instance needs to be provided when sending a password reset email or a verification email. It can be created with the associated ActionCodeSettings.Builder class which contains the following methods:

The following example illustrates how to send an email verification link that will open in a mobile app first. The deep link will contain the continue URL payload http://www.example.com/verify?uid=1234.

val auth = Firebase.auth
val user = auth.currentUser!!

val url = "http://www.example.com/verify?uid=" + user.uid
val actionCodeSettings = ActionCodeSettings.newBuilder()
    .setUrl(url)
    .setIOSBundleId("com.example.ios")
    // The default for this is populated with the current android package name.
    .setAndroidPackageName("com.example.android", false, null)
    .build()

user.sendEmailVerification(actionCodeSettings)
    .addOnCompleteListener { task ->
        if (task.isSuccessful) {
            Log.d(TAG, "Email sent.")
        }
    }
MainActivity.kt

FirebaseAuth auth = FirebaseAuth.getInstance();
FirebaseUser user = auth.getCurrentUser();

String url = "http://www.example.com/verify?uid=" + user.getUid();
ActionCodeSettings actionCodeSettings = ActionCodeSettings.newBuilder()
        .setUrl(url)
        .setIOSBundleId("com.example.ios")
        // The default for this is populated with the current android package name.
        .setAndroidPackageName("com.example.android", false, null)
        .build();

user.sendEmailVerification(actionCodeSettings)
        .addOnCompleteListener(new OnCompleteListener<Void>() {
            @Override
            public void onComplete(@NonNull Task<Void> task) {
                if (task.isSuccessful()) {
                    Log.d(TAG, "Email sent.");
                }
            }
        });
MainActivity.java

Configuring Firebase Hosting links

Firebase Authentication uses Firebase Hosting when sending a link that is meant to be opened in a mobile application. In order to use this feature, Hosting links need to be configured in the Firebase console.

1. Configuring Android applications:

   1. If you plan on handling these links from your Android application, your app's package name needs to be specified in the Firebase console project settings. In addition, the SHA-1 and SHA-256 of the application certificate need to be provided.
   2. You will also need to configure the intent filter for the deep link in your AndroidManifest.xml file.
   3. For more on this, refer to Receiving Android Hosting links instructions.

2. Configuring iOS applications:

   1. If you plan on handling these links from your iOS application, you will need to configure the Hosting link domain as an Associated Domain in your application capabilities.
   2. For more on this, refer to Receiving iOS Hosting links instructions.

Handling email actions in a web application

You can specify whether you want to handle the action code link from a web application first and then redirect to another web page or mobile application after successful completion, provided the mobile application is available. This is done by calling setHandleCodeInApp(false) in the ActionCodeSettings.Builder object. While an iOS bundle ID or Android package name are not required, providing them will allow the user to redirect back to the specified app on email action code completion.

The web URL used here, is the one configured in the email action templates section. A default one is provisioned for all projects. Refer to customizing email handlers to learn more on how to customize the email action handler.

In this case, the link within the continueUrl query parameter will be an Hosting link whose payload is the URL specified in the ActionCodeSettings object.

When handling email actions such as email verification, the action code from the oobCode query parameter needs to be parsed from the deep link and then applied via applyActionCode for the change to take effect, i.e. email to be verified.

Handling email actions in a mobile application

You can specify whether you want to handle the action code link within your mobile application first, provided it is installed. If the link is clicked from a device that does not support the mobile application, it is opened from a web page instead. This is done by calling setHandleCodeInApp(true) in the ActionCodeSettings.Builder object. The mobile application's Android package name or iOS bundle ID will also need to be specified.

The fallback web URL used here, when no mobile app is available, is the one configured in the email action templates section. A default one is provisioned for all projects. Refer to customizing email handlers to learn more on how to customize the email action handler.

In this case, the mobile app link sent to the user will be a Hosting link whose payload is the action code URL, configured in the Console, with the query parameters oobCode, mode, apiKey and continueUrl. The latter will be the original URL specified in the ActionCodeSettings object. The action code can be applied directly from a mobile application similar to how it is handled from the web flow described in the customizing email handlers section.

When handling email actions such as email verification, the action code from the oobCode query parameter needs to be parsed from the deep link and then applied via applyActionCode for the change to take effect, i.e. email to be verified.