Added scope property to Credentials

[cocojoe]

No description provided.

[cocojoe]

@lbalmaceda See if the scope property doc makes sense

[lbalmaceda]

I think it's ok, my only doubt is if I as a dev would need the scope to be a String[] rather than just a String, for easy checking of granted scopes.

[hzalaz]

@lbalmaceda it will be [String] 😜 .

@cocojoe expanding what @lbalmaceda said we could have a method to help check that the returned scopes contains a list of scopes like

let requested = "openid profile email read:user post:ticket"
...
let missing: [String] = credentials.rejected(from: requested)

but it could be material of another PR so Android is in sync too

[cocojoe]

Agree a helper would be nice, as this has been approved already will merge and raise another PR.