Ktor OAuth, cant set User session when I have token

So im trying to set up a OAuth way of logging in my Ktor program. Quite new to Kotlin and Ktor so I am having a hard time. I am able to create a token and I get sent to the "get("/callback")" part of the plugin generated code.

But as i try to run the line

call.sessions.set(UserSession(principal!!.state!!, principal.accessToken))

I get

"Session data for type `class com.example.plugins.UserSession` was not registered"

I have tried to understand what is going wrong but at this point I have no clue. UserSession wants two strings, but if i replace my two inputs with just

`UserSession("random string", "random string")`

I get the same error.

My values for principal are

accessToken = ya29.a0AVvZVsrXsX2_6eu-3N_1ITbT3i-7QIvytMtJvu0zU93NyPoWBPMM42k1Ypf9VQrsrK_FygNEAhwdfJUbSZem7_UQSBNupOaLbsm9NB0QJl6rZt3-0cmQMDvUVG_oIYl8rorpooyekPWMVPyMYQSfBpyjHnfeaCgYKAYESARESFQGbdwaIaU-pvIfQ3cEVeXbd-4jRlg0163

state = 59f45f0e9fcb6ebb

The snipit of what where the code runs.

 get("/callback") {
            val principal: OAuthAccessTokenResponse.OAuth2? = call.principal()
            call.sessions.set(UserSession(principal!!.state!!, principal.accessToken)) //throws error
            val redirect = redirects[principal.state!!]
            call.respondRedirect(redirect!!)
        }

Solution

I think you missed configuring your install(Sessions) block, to use sessions, you have to pass the session id to the client, this can be done either using cookies or header:

install(Sessions) {
    cookie<UserSession>("user_session", directorySessionStorage(File("build/.sessions"))) {
        cookie.path = "/"
        cookie.maxAgeInSeconds = 10
    }
}

OR:

install(Sessions) {
    header<UserSession>("user_session", directorySessionStorage(File("build/.sessions")))
}

Choose whatever you think is good for you. For more info, visit the documentation