> For the complete documentation index, see [llms.txt](https://cramiumlabs.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cramiumlabs.gitbook.io/docs/sdk-mpc-android/usage-guide-for-an-mpc-wallet-app/passkey.md).

# Passkey

The Kotlin Android Passkey module ensures secure and streamlined user authentication and registration using modern passkey technology. It provides a set of methods to verify a user’s existence, authenticate users, and register new users.

#### 1. **isUserExist**

The **isUserExist()** method checks whether a user with the provided username already exists in the system. It returns a Flow emitting a Boolean value indicating the existence status.

**Example**:

```kotlin
    fun main() {
    // Check if the user "john_doe" exists
        isUserExist("john_doe").collect { exists ->
            println("User exists: $exists")
        }
    }
```

#### 2. authenticate

The **authenticate()** method initiates the passkey authentication process for a user. It accepts the username and the activity context to start the authentication flow. The method returns a Flow that emits an AuthVerifyResponse containing details of the authentication result.

**Example:**

```kotlin
fun main() {
    // Authenticate user "john_doe" within the current activity context
    authenticate("john_doe", this).collect { response ->
        println("Authentication successful: $response")
    }
}

```

#### 3. register

The **register()** method starts the passkey-based registration process for a new user. It takes the username and the activity context, then returns a Flow emitting a RegisterVerifyResponse with the registration details.

**Example:**

```kotlin
fun main() {
    // Register a new user "john_doe"
    register("john_doe", this).collect { response ->
        println("Registration successful: $response")
    }
}
```