Taken from PR 199922 with slight modifications.
Proposed commit message:
new port: security/rubygem-rack-oauth2 OAuth 2.0 Server & Client Library. WWW: https://github.com/nov/rack-oauth2 PR: 199922 Submitted by: Torsten Zuehlsdorff <ports@toco-domains.de> Approved by: swills (mentor), mat (mentor)