Sign In with Email/Phone Number

Our Android SDK offers the easiest way to verify email/phone numbers in your android app. You can simply call a function and it does most of the heavy lifting and authentication for you.

Concepts: Learn about how Sign in with Email/Phone Number works.


Verifying email and phone number in your mobile app using our Android SDK consists of the following steps:

  1. Import Cotter

  2. Call Cotter's Login function

  3. Receive user's email or phone number, and whether or not it's verified

What you're building


  1. Register URL Scheme: Cotter's authentication will redirect back to your application using this URL scheme.

  2. Call Cotter's Login function: This function will handle the WebView, verifying phone number or email, and request the identity from Cotter's server.

  3. Receive the Token: Include the returned token and email/phone number in your server

Step 1: Import Cotter as a dependency

Add JitPack repository your project level build.gradle at the end of repositories.

allprojects {
		repositories {
			maven { url '' }

Add the Cotter's SDK as a dependency in your app level build.gradle .

android {
  compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8

dependencies {
  implementation 'com.github.cotterapp:android-sdk:0.3.0'

Check the latest version here

Then sync your gradle files.

Step 2: Initialize Cotter with your API keys

Initialize Cotter with your API_KEY_ID . Call the function below in your MainActivity


For example:
public class MainActivity extends AppCompatActivity {

    protected void onCreate(Bundle savedInstanceState) {


Step 3: Register a URL Scheme

You also need to decide a callback URL scheme that you want to use. If your app's package name is com.example.myapplication then you should use something like this for your URL Scheme callback.


Make sure your URL scheme (the front part before ://) doesn't have an underscore or other special characters. To test it out, enter your Redirect URL here:

This URL scheme will be called when Cotter's verification is done and want to go back to your app. Read more about Android deep-linking.

You need to register this URL Scheme to receive the callback. Add the following in your AndroidManifest.xml . Check the example in the example's Github repo.

<activity android:name="" android:exported="true">
        <action android:name="android.intent.action.VIEW"/>
        <category android:name="android.intent.category.DEFAULT"/>
        <category android:name="android.intent.category.BROWSABLE"/>
        <!--   This example is for: com.example.myapplication://auth_callback    -->
        <!--   Change it to your own url    -->
        <data android:scheme="com.example.myapplication" 
<!--   TO HERE    -->

Step 4: Call Cotter's Login function

To open up Cotter's Login screen, you can either have your user input their email or phone number inside Cotter's screen, or you can provide a text input where your users can enter their email / phone, and you can pass that to Cotter's screen.

a) To login and enter the email or phone number in Cotter's window:

 // Provide Context and the URL Scheme
 Cotter.newIdentity(this, "com.example.myapplication://auth_callback")
        "EMAIL",             // EMAIL or PHONE
        this,                // Context
        Dashboard.class);    // Callback Class

b) To login with the email or phone number that your user entered in your app:

// Provide Context and the URL Scheme
 Cotter.newIdentity(this, "com.example.myapplication://auth_callback")
    .loginWithInput( // Context
       "EMAIL",                     // EMAIL or PHONE
       input.getText().toString(),  // User's email
       this,                        // Context
       CallbackActivity.class);     // Callback Class

To send code/link via SMS or WhatsApp, you'll need to add some balance to you project in the Dashboard.

You need to provide a class to redirect to when Cotter's email/phone number verification is complete.

Try it now! You can check if it works so far by invoking the login function above on a button click. It should load Cotter's Authentication page on a WebView.

Step 5: Receive the Token

In your CallbackActivity class, receive the token from the intent inside onCreate using this function.

String resp = IdentityManager.handleResponse(getIntent());
if (resp != null) {
    Log.i("Login Response: ", resp);
String error = IdentityManager.handleError(getIntent());
if (error != null) {
    Log.i("Login Error: ", error);

For example, if your CallbackActivity class is called Dashboard:

public class Dashboard extends AppCompatActivity {

    protected void onCreate(Bundle savedInstanceState) {
        // Handle response here
        String resp = IdentityManager.handleResponse(getIntent());
        if (resp != null) {
            Log.i("Login Response: ", resp);
        // Handle error here 
        String error = IdentityManager.handleError(getIntent());
        if (error != null) {
            Log.i("Login Error: ", error);

The resp will consist of the following JSON Object as a string.

  "identifier": {
    "ID": "f4286df9-a923-429c-bc33-5089ffed5f68",
    "created_at": "2020-07-21T22:53:21.211367Z",
    "updated_at": "2020-07-21T22:53:21.211367Z",
    "deleted_at": "0001-01-01T00:00:00Z",
    "identifier": "", // User's email
    "identifier_type": "EMAIL",
    "device_type": "BROWSER",
    "device_name": "Mozilla/5.0 (Linux; Android 9; Android SDK built for x86 Build/PSR1.180720.075) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Mobile Safari/537.36",
    "expiry": "2020-08-20T22:53:21.19705Z",
    "timestamp": "2020-07-21T22:53:21.19705Z"
  "oauth_token": {
    "access_token": "eyJhbGciOiJFUz...", // Validate this access token
    "id_token": "eyJhbGciOiJFUzI1...",
    "refresh_token": "27944:lb31DY5pG229n...",
    "expires_in": 3600,
    "token_type": "Bearer",
    "auth_method": "OTP"
  "token": {...},
  "user": {
    "ID": "643a42c7-316a-4abe-b27e-f4d0f903bfea", // Cotter uesr ID
    "identifier": "",

This JSON object contains 3 objects, identifier , oauth_token and user .

  • The identifier object contains information about the user's email or phone number, device type and name, and expiry.

  • The oauth_token contains an access_token that you can validate in your backend.

  • The user contains the User object in Cotter, which includes a "Cotter User ID". You should associate your user with this Cotter User ID for reference.

You should include this JSON Object into your call to your backend for Login or Registration. Your backend should then verify that the access token is valid.

Validating Cotter's Access Token

Checkout how to verify the OAuth Tokens from Cotter here:

Verifying JWT Tokens

🎉 You're done!

Securing your Project

Since you'll be using your API Key from a front-end website or mobile app, your API_KEY_ID is exposed to anyone inspecting your code. Here are some ways to prevent abuse:

Next Steps

Implement Trusted Devices

Sign In with Device

Add Biometric/PIN


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