Declare GIT_CREDTYPE_SSH_MEMORY to have consistent API independently of
whether libgit2 was built with or without in-memory key passing support.
Or rather, to have it at all since build-time definitions are not stored
in headers.
Instead of having it set in a different place from every other callback,
put it the main structure. This removes some state from the remote and
makes it behave more like clone, where the constructors are passed via
the options.
Instead of spreading the data in function arguments, some of which
aren't used for ssh and having a struct only for ssh, use a struct for
both, using a common parent to pass to the callback.
If the certificate validation fails (or always in the case of ssh),
let the user decide whether to allow the connection.
The data structure passed to the user is the native certificate
information from the underlying implementation, namely OpenSSL or
WinHTTP.
* Move the transport registration mechanisms into a new header under
'sys/' because this is advanced stuff.
* Remove the 'priority' argument from the registration as it adds
unnecessary complexity. (Since transports cannot decline to operate,
only the highest priority transport is ever executed.) Users who
require per-priority transports can implement that in their custom
transport themselves.
* Simplify registration further by taking a scheme (eg "http") instead
of a prefix (eg "http://").
git allows you to set which paths to use for the git server programs
when connecting over ssh; and we want to provide something similar.
We do this by providing a factory function which can be set as the
remote's transport callback which will set the given paths upon
creation.
When linking against libssh2, create the transport.h such that it
contains its definition for custom crypto and keyboard-interactive
callbacks.
If we don't link against libssh2, create an equivalent signature which
has void pointers instead of pointers to libssh2 structures.
This would be one way to fix#2438.
The callback-based method of listing remote references dates back to the
beginning of the network code's lifetime, when we didn't know any
better.
We need to keep the list around for update_tips() after disconnect() so
let's make use of this to simply give the user a pointer to the array so
they can write straightforward code instead of having to go through a
callback.
The names from libssh2 are somewhat obtuse for us. We can simplify the
usual key/passphrase credential's name, as well as make clearer what the
custom signature function is.
Key-based authentication also needs an username, so include it in each
one.
Also stop assuming a default username of "git" in the ssh transport
which has no business making such a decision.
