Hello, how can I retrieve a session arbitrarily? T...

# ktor

[Matthieu Stombellini]

Hello, how can I retrieve a session arbitrarily? That is, I have sessions using a header, everything being stored on the server, the client only transmits a session ID in the header. I need to be able to retrieve the session with its ID without the header being in the call. How can I do that? In other words, how can I retrieve any session given only the session's ID?

[Casey Brooks]

Ktor’s built-in session feature has support for storing only the session ID in a cookie, which is enabled by providing a session storage (such as directorySessionStorage, but you can write your own storage mechanism as well). If you do not provide session storage, then the entire session contents are serialized and saved in that cookie instead. https://ktor.io/servers/features/sessions.html#directorySessionStorage

You can also customize whether it expects that session ID to be in a cookie or a specified header https://ktor.io/servers/features/sessions.html#cookie-vs-header

[Casey Brooks]

As HTTP (and thus ktor) is stateless, you must provide either the cookie or a session header in a request, otherwise the server has no way of knowing who “you” are. However, a stateful protocol like websockets (which Ktor also supports) does allow you to maintain a persistent session without needing to repeatedly send the same session IDs with each request

[Matthieu Stombellini]

Hi, I know all of this, the issue here is that I'm getting the ID in another way (through a state parameter in the URL, as I'm trying to retrieve my state upon an OIDC Provider's redirection to my server), not through the header

[Casey Brooks]

You’d probably want to find that state parameter from the call set it to the normal header/cookie session in the request handler, since query parameters are not persistent. call.sessions.getOrSet is helpful here

get("/redirect") {
    val session: AppSession = call.sessions.getOrSet {
        val sessionId = call.parameters["state"]!!
        AppSession(sessionId)
    }
}

[arjun]

interesting topic. just to dig more, how does this work in a multi node/container setup ?

[Casey Brooks]

If the sessions are stored in a database that is shared by all nodes (as opposed to in-memory or a file which is local to each node), then it should be fairly transparent

[arjun]

ok.. i ll figure out how to configure session storage