Modify object when calling alastria/alastriaSession

[VictorNS69]

At the moment, we are using a simple string in the call to alastria/alastriaSession, but we are using application/json as MediaType.

It should be an object with only one key (jwt) and use the application/json MediaType.

Example:

{
    "jwt": "<the signed Alastria Session JWT as a String>"
}