• Added service_account.Credentials.project_id. (#187)
• Move read-only methods of credentials.Scoped into new interface credentials.ReadOnlyScoped. (#195, #196)
• Make compute_engine.Credentials derive from ReadOnlyScoped instead of Scoped. (#195)
• Fix App Engine's expiration calculation (#197)
• Split crypt module into a package to allow alternative implementations. (#189)
• Add error message to handle case of empty string or missing file for GOOGLE_APPLICATION_CREDENTIALS (#188)