Recently I have finished some work on the TeamCity Crowd Plugin.
This plugin enables TeamCity to use Crowd for user authentication. It could be used in places where Crowd is used to manage access to other products (for example Atlassian JIRA or Confluence). Thanks to this plugin the same user base will be able to access TeamCity.
The plugin is open Source, available on GitHub, binary build downloadable on BinTray.
TeamCity Crowd Plugin is using Atlassian Java REST Client to connect to Crowd. More detailed description of functionality on GitHub.
Please do get in touch with feedback/improvements.
Greg