This changes the logic of `credentialsCallback` so that it takes the
`allowedTypes` passed on by `git2go` into account. Reason for this
change is because this prepares it to work with `v33`, but also
because it can provide better guidance when `libgit2` has been
compiled with a different configuration, which e.g. doesn't
allow for "in-memory SSH keys".
Because `AuthOptions#Identity` now gets validated by the callback
and go-git does its own validaiton, the check has been removed
from `Validate` (and now does a simple check if the fields are set).
Signed-off-by: Hidde Beydals <hello@hidde.co>
This commit moves the previous `AuthStrategy` wiring to a more generic
`AuthOptions`, breaking free from implementation specific details in
the `git` package.
Signed-off-by: Hidde Beydals <hello@hidde.co>