vcs: Only allow 'pull' actions on shadow repositories.
We are exposing the shadow repositories of pull requests to allow easy CI integration
or users to access the pull request shadow repo for investigating on it. But we don't
want someone/something to push changes to a shadow repository.
vcs: Use key lookup to explode if key is not available.
The key has to be in the dictionary, otherwise something changed in the code
and expoding here is better than hiding the error.
vcs: Minimal change to expose the shadow repository
Based on my original research, this was the "minimal" starting point. It shows
that three concepts are needed for the "repo_name":
* From the security standpoint we think of the shadow repository having the same
ACL as the target repository of the pull request. This is because the pull
request itself is considered to be a part of the target repository.
Out of this thought, the variable "acl_repo_name" is used whenever we want to
check permissions or when we need the database configuration of the
repository. An alternative name would have been "db_repo_name", but the usage
for ACL checking is the most important one.
* From the web interaction perspective, we need the URL which was originally
used to get to the repository. This is because based on this base URL commands
can be identified. Especially for Git this is important, so that the commands
are correctly recognized.
Since the URL is in the focus, this is called "url_repo_name".
* Finally we have to deal with the repository on the file system. This is what
the VCS layer deal with normally, so this name is called "vcs_repo_name".
The original repository interaction is a special case where all three names are
the same.
When interacting with a pull request, these three names are typically all
different.
This change is minimal in a sense that it just makes the interaction with a
shadow repository barely work, without checking any special constraints yet.
This was the starting point for further work on this topic.
Martin Bornhold
