https://developer.linkedin.com/documents/code-samples
Using the above PHP code sample, I can log in to my user profile as expected, (after creating the required "application" and getting the API KEY and SECRET, of course.)
However the $user object returned by the Fetch() function is null, so I do not have access to the profile content via the code, such as the $user->firstname and $user->lastname, etc.
FYI: This question was asked before and not answered: LinkedIn Code Sample not returning ay data