Out of the box, the embedded Web server of Orthanc supports HTTP Basic access authentication. To configure user authentication for Orthanc, make sure to properly set the following configuration options:
RegisteredUsers, assign a username and a password to all your users.
Once a user has logged in, she will have full access, in read-write mode, to all the features offered by the REST API of Orthanc. This built-in mechanism might be of limited usefulness in enterprise scenarios, for which you would need features such as:
Depending on your scenario, you can consider the following options:
OrthancPluginRegisterIncomingHttpRequestFilter(). This solution is potentially useful if you wish to integrate with an LDAP server.