Implement creation of self signed jwt for assertion based auth.
Fix bug in self signed JWT creation.  The header must contain the cert thumbprint.  The jwt-simple lib doesn't provide a way to do that.  Switching to customer implementation.
This should have been part of the last commit, 354704bba47babd3de39583a6d86fc6965a4897a.
Get basic cert auth happy path implemented.
Merge branch 'dev' into cert_auth

Conflicts:
	test/util/util.js
Update basic self-signed-jwt test to actually check that the returned jwt matches what was expected given static inputs.
Complete self-sign-jwt validation code and tests.
Add end to end tests for client assertion flow.
Add sample for certificate/client assertion flow.