$.ajax({
  url: "http://localhost:5984/_session",
  type: "POST",
  data: {
    username: "myUsername",
    password: "myPassword",
  },
  success: function (result) {
    console.log(result);
  },
  error: function (err) {
    console.log(err);
  },
});

{ name: "myUsername", ok: true, roles: [ "someRoles" ] }

$.ajax({
  url: "http://localhost:5984/_session",
  type: "GET",
  success: function (result) {
    console.log(result);
  },
});

{
  info: { authentication_db: "_users", authentication_handlers: […] },
  ok: true,
  userCtx: { name: null, roles: [] }
}