Hello. I managed to set up JWT authentication in ktor. It works. However I dont see how to get the c...

# ktor

[pascal_le_merrer]

Hello. I managed to set up JWT authentication in ktor. It works. However I dont see how to get the claims containd in the token when processing a request. How can I get them?

[Pedro Flores]

If I'm not mistaken, you can get them inside your call by accessing the Principal property

[pascal_le_merrer]

That's what I did before replacing basic auth with JWT.
I got it using

val principal: UserIdPrincipal? = call.authentication.principal<UserIdPrincipal>()

But with JWT, call.authentication.principal is null

[pascal_le_merrer]

I found the solution. I have to get the claim like this:

val principal: JWTPrincipal? = call.authentication.principal<JWTPrincipal>()
return principal!!.payload.getClaim("my_claim").asString()

[Pedro Flores]

Glad that you've found it, on a test I wrote i'm able to get it directly from the ApplicationCall.principal, but I don't know how your validate lambda is implemented

[pascal_le_merrer]

I’m interested in your validate lambda, @Pedro Flores. Could you post it please?

[pascal_le_merrer]

Mine looks like this:

fun validateCredential(jwtCredential: JWTCredential): Principal? {

    val sessionId = jwtCredential.payload.getClaim("sessionId").asString()

    if (isValidSessionId(cuid, sessionId)) {
        return JWTPrincipal(jwtCredential.payload)
    }

    return null
}

[Pedro Flores]

Well it’s quite similar, the difference is that I have an extended Principal but still it should be working as the documentation intended :)

[pascal_le_merrer]

That’s the point I missed. It’s much simpler with a class extending Principal. Thanks @Pedro Flores! 👍