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kotlinlang

```open class SimpleJWT(val secret: String) {
    private val algorithm = Algorithm.HMAC256(secret)
    val verifier = JWT.require(algorithm).build()
    fun sign(name: String): String = JWT.create().withClaim("name", name).sign(algorithm)
}
fun Application.module() {
    val simpleJwt = SimpleJWT("my-super-secret-for-jwt")
    install(Authentication) {
        jwt {
            verifier(simpleJwt.verifier)
            validate {
                UserIdPrincipal(it.payload.getClaim("name").asString())
            }
        }
    }
    // ...
}```

The withClaim method allows you to add additional information to your JWT Token (see <https://jwt.io/> for more info).

The UserIdPrincipal will be a provided Principal to your ApplicationCalls if you're properly authenticated.

Can you please elaborate UserIdPrincipal?

See for example on <https://ktor.io/samples/feature/auth.html>, you can get info about the current logged user. For example there you can access the claims you’ve setted in the JWT token to identify your user/ do some operations based on role values for example