Add authentication for WebSocket API using PAM and JWT

[Uggah]

Idea: a /auth or /login HTTP endpoint. In the message body the parameters of the authentication are transferred. Then, a JWT is returned with which the user can authenticate themselves to the WebSocket API (i.e. "/ws?token=ey...").

The payload should look like the following:

Request:

{
    "auth_method": "PAM",
    "username": "username",
    "password": "password",
}

Response:

{
    "jwt": "ey..."
}

This way, other authentication methods can be implemented later on. For example:

Request:

{
    "auth_method": "OIDC"
    "token": "ey..."
}

[Uggah]

Resolved in #14