The @SipApplicationKey annotation is used when the application wants to associate
the incoming request (and SipSession) with a certain SipApplicationSession
The method annotated with the @SipApplicationKey annotation MUST have the
following restrictions:
- It MUST be public and static
- It MUST return a String
- It MUST have a single argument of type SipServletRequest
- It MUST not modify the SipServletRequest passed in
If the annotated method signature does not comply with the first three rules,
deployment of such an application MUST fail.