Android Verified Email using Credential Manager Skill

Fundamentals

  • Overview of Digital Credentials: Learn about cryptographically verifiable documents and the role of Credential Manager.
  • Glossary: Definitions for dcql_query, UserInfoCredential, and GetDigitalCredentialOption.

Standards & Examples

Requirements

  • SDK Version: Minimum SDK 28 (Android 9) is required.
  • GMS Version: Google Play services version 25.49.x or higher.

Use Cases

Email verification is applicable for the following use cases:

  • Account Creation/Sign-up: Remove friction by skipping manual email verification.
  • Account Recovery: Securely verify email ownership during recovery flows.
  • Re-authentication: Versatile verification for high-risk actions, independent of the initial sign-in method.

Limitations & Nuances

  • Workspace Accounts: Google does not issue verifiable credentials for Google Workspace Accounts.
  • Freshness: For non-@gmail.com addresses, Google verifies the email at account creation but there is no freshness claim; implement an additional challenge like an OTP.

Scope & Pre-requisites

Crucial: This skill focuses exclusively on the Android client-side integration. It does not implement the app's server-side cryptographic validation logic. Server-side validation of the returned credential is required for security and must be implemented in your backend.

Codebase exploration for Use Cases

Get started with the following queries in project source code to find relevant screens with different use cases to implement verified email:

  • SignUpScreen
  • "Email address"
  • "Recover Account"
  • "Account Recovery"
  • "Forgot password?"
  • "Delete Account"

Identifying Integration Points

To implement this feature effectively, you must first locate the relevant flows in your codebase. To initiate, start with the following strategies to cater to different use cases using verified email:

1. Search for Navigation Routes

If your app uses Navigation, search for routes or destinations related to authentication:

Look for:

  • Keywords: signup, registration, create_account, forgot_password, recovery, verify_email.
  • Code Pattern: Search for NavHost or composable destinations using these strings.

2. Locate Authentication ViewModels

Find the business logic handling user attributes and account creation, account recovery:

  • Keywords: SignUpViewModel, AuthViewModel, RegistrationRepository.
  • Code Pattern: Look for methods like onCreateAccount, onRecoverAccount, or validateEmail.

3. Find instances of reauthentication for sensitive actions

For reauthentication use cases, find areas where users perform sensitive actions:

  • Keywords: ChangePassword, UpdatePayment, DeleteAccount, UpdateDetails, EditUserDetails

Important pointers for Implementation

  • Construct a Digital Credential Request and present it to the user.
  • Make sure to follow the request JSON structure as mentioned in documentation.
  • While presenting the request to the user, check if result credential is DigitalCredential and credential.credentialJson as responseJsonString
  • Parse the response from the client.
  • Offer a passkey creation option if one is not already present.
  • Assume a local SdJwtParser to parse raw SD-JWT and return a JSONObject.
  • Use a VerifiedUserInfo data class to store the parsed name and email.
  • Leave a TODO for developers to handle the app's server-side validation and parsing.
  • Direct users to the home screen after API call success and show a snackbar with user details for reference purpose only.

Add dependencies

In your app's build.gradle file, add the following dependencies for Credential Manager:

Kotlin

dependencies {
    implementation("androidx.credentials:credentials:1.7.0-alpha02")
    implementation("androidx.credentials:credentials-play-services-auth:1.7.0-alpha02")
}

Groovy

dependencies {
    implementation "androidx.credentials:credentials:1.7.0-alpha02"
    implementation "androidx.credentials:credentials-play-services-auth:1.7.0-alpha02"
}

Initialize Credential Manager

Use your app or activity context to create a CredentialManager object.

// Use your app or activity context to instantiate a client instance of
// CredentialManager.
private val credentialManager = CredentialManager.create(context)

Construct the Digital Credential request

To request a verified email, construct a GetCredentialRequest containing a GetDigitalCredentialOption. This option requires a requestJson string formatted as an OpenID for Verifiable Presentations (OpenID4VP) request.

The OpenID4VP request JSON must follow a specific structure. The current providers support a JSON structure with an outer "digital": {"requests": [...]} wrapper.

    val nonce = generateSecureRandomNonce()

    // This request follows the OpenID4VP spec
    val openId4vpRequest = """
{
  "requests": [
    {
      "protocol": "openid4vp-v1-unsigned",
      "data": {
        "response_type": "vp_token",
        "response_mode": "dc_api",
        "nonce": "$nonce",
        "dcql_query": {
          "credentials": [
            {
              "id": "user_info_query",
              "format": "dc+sd-jwt",
               "meta": { 
                  "vct_values": ["UserInfoCredential"] 
               },
              "claims": [ 
                {"path": ["email"]}, 
                {"path": ["name"]},  
                {"path": ["given_name"]},
                {"path": ["family_name"]},
                {"path": ["picture"]},
                {"path": ["hd"]},
                {"path": ["email_verified"]}
              ]
            }
          ]
        }
      }
    }
  ]
}
"""

    val getDigitalCredentialOption = GetDigitalCredentialOption(requestJson = openId4vpRequest)
    val request = GetCredentialRequest(listOf(getDigitalCredentialOption))

Next, wrap the openId4vpRequest JSON in a GetDigitalCredentialOption, create a GetCredentialRequest, and call getCredential().

Present the request to the user

Present the user with the request, using the Credential Manager built-in UI.

try {
    // Requesting Digital Credential from user...
    val result = credentialManager.getCredential(activity, request)

    when (val credential = result.credential) {
        is DigitalCredential -> {
            val responseJsonString = credential.credentialJson

            // Successfully received digital credential response.

            // Next, parse this response and send it to your server.
            // ...
        }

        else -> {
            // handle Unexpected State() - Up to the developer
        }
    }
} catch (e: Exception) {
    // handle exceptions - Up to the developer
}

Parse the response on the client

After receiving the response, you can perform a preliminary parse on the client. This is useful for immediately updating the UI, for example, by showing the user's name.

The following code extracts the raw Selective Disclosure JWT (SD-JWT) and uses a helper to decode its claims.

// 1. Parse the outer JSON wrapper to get the `vp_token`
val responseData = JSONObject(responseJsonString)
val vpToken = responseData.getJSONObject("vp_token")

// 2. Extract the raw SD-JWT string
val credentialId = vpToken.keys().next()
val rawSdJwt = vpToken.getJSONArray(credentialId).getString(0)

// 3. Use your parser to get the verified claims
// Server-side validation/parsing is highly recommended.

// Assumes a local parser like the one in our SdJwtParser.kt sample
val claims = SdJwtParser.parse(rawSdJwt)
Log.d("TAG", "Parsed Claims: ${claims.toString(2)}")

// 4. Create your VerifiedUserInfo object with REAL data
val userInfo = VerifiedUserInfo(
    email = claims.getString("email"),
    displayName = claims.optString("name", claims.getString("email"))
)

Handle the response

The Credential Manager API will return a DigitalCredential response.

The following is an example of what the raw responseJsonString looks like, and what the claims look like after parsing the inner SD-JWT where you get additional metadata as well along with verified email:

/*
// Example of the raw JSON response from credential.credentialJson:
{
  "vp_token": {
    // This key matches the 'id' you set in your dcql_query
    "user_info_query": [
      // The SD-JWT string (Issuer JWT ~ Disclosures ~ Key Binding JWT)
      "eyJhbGciOiJ...~WyI...IiwgImVtYWlsIiwgInVzZXJAZXhhbXBsZS5jb20iXQ~...~eyJhbGciOiJ..."
    ]
  }
}

// Example of the parsed and verified claims from the SD-JWT on your server:
{
  "cnf": {
    "jwk": {..}
  },
  "exp": 1775688222,
  "iat": 1775083422,
  "iss": "https://verifiablecredentials-pa.googleapis.com",
  "vct": "UserInfoCredential",
  "email": "jane.doe.246745@gmail.com",
  "email_verified": true,
  "given_name": "Jane",
  "family_name": "Doe",
  "name": "Jane Doe",
  "picture": "http://example.com/janedoe/me.jpg",
  "hd": ""
}
 */

Server-side validation for account creation

For verification, your application must send the full responseJsonString to your server for cryptographic validation before creating an account or logging the user in.

The validation on the server must achieve the following:

  • Verify issuer: Ensure the iss (issuer) field matches https://verifiablecredentials-pa.googleapis.com.
  • Verify signature: Check the signature of the SD-JWT using the public keys (JWKs) available at https://verifiablecredentials-pa.googleapis.com/.well-known/vc-public-jwks.

For full security, make sure that you also validate the nonce to prevent replay attacks.

try {
    // Send the raw credential response and the original nonce to your server.
    // Your server must validate the response. createAccountWithVerifiedCredentials
    // is a custom implementation per each RP for server side verification and account creation.
    val serverResponse = createAccountWithVerifiedCredentials(responseJsonString, nonce)

    // Server returns the new account info (e.g., email, name)
    val claims = JSONObject(serverResponse.json)

    val userInfo = VerifiedUserInfo(
        email = claims.getString("email"),
        displayName = claims.optString("name", claims.getString("email"))
    )

    // handle response - Up to the developer
} catch (e: Exception) {
    // handle exceptions - Up to the developer
}

An optional but highly recommended next step after provisioning an account is to immediately create a passkey for that account. This provides a secure, passwordless method for the user to sign in. This flow is identical to a standard passkey registration.

For the flow to work on a WebView, developers should implement a JavaScript bridge (JS Bridge) to facilitate the handoff. This bridge allows the Webview to signal the native app, which can then perform the actual call to the Credential Manager API.

Critical Security Guidelines

To maintain the integrity of the email verification flow, the following security requirements are mandatory:

  • Server-side Validation : Never trust claims parsed on the client for security-sensitive operations like account creation. Send the complete, raw responseJsonString and the original nonce to the app's server for full verification.
  • Nonce Integrity : Generate a unique, cryptographically secure nonce for every request and never reuse a nonce across multiple requests to prevent replay attacks.
  • Cryptographic Checks : The app's server must validate the issuer (iss) field, the SD-JWT signature, and the presenter identity using the cnf field.