This is partly covered by T4705 and T4245 but has a slightly different use case.
We serve repositories from multiple URLs: `https://git..../reponame` and `https://git..../ro/reponame`. Each of these has a different purpose. The first is the main URI, the second is a read only replica which doesn't require kerberos authentication. We're also considering some other special prefixes (/backdoor/, etc.). For a variety of reasons we can not serve the read/write version to phabricator (as an externally hosted repo). This means that repository auto-detection doesn't work.
```
The remote URI for this working copy is
"https://git.../ro/reponame".
No repositories matched the query. Check that your configuration is
correct, or use "repository.callsign" to select a repository explicitly.
```
Since we may many hundreds of repositories manually adding a .arcconfig to each one is time consuming an expensive. We have managed to eliminate the need for `phabricator.uri` and `base` by setting them in `/etc/arcconfig`. Obviously for callsigns this approach won't work. We'd like to be able to list server-set a set of alternate URIs that map the same repository.
This is also useful if a repo gets renamed or moved to a different host.