No required/optional monikers for SSA

[Pamela Dingle]

There are specific parts of the SSA which if not present should cause an error. The spec needs to note which parts of the SSA are necessary and indicate the validation in the examples. Specifically, an SSA without at least one valid redirect_uri must be rejected.

[Ralph Bragg]

Good shout - we don't allow SSAs to be created that don't have at least one redirect URI but we should make it explicit in the specification should someone want to copy it.