It's possible to configure Archivesspace API to be accessed at a specific path. For example, simesite.edu/api, where all routes are appended to the end of the path provided. The way that requests are made to the Archivesspace instance the path is currently being ignored even if it's part of the "ArchivesSpace API Prefix" used to make requests to an Archivesspace API. I think you should be allowed to include a path to the prefix.
Allow users to include a path in their "ArchivesSpace API Prefix".
An update to the Drupal\archivesspace\ArchivesSpaceSession\login function will be needed.
Active
1.0
Code
Adding a patch for this since I have an immediate need for this. It's the same change made to the merge request above.