Re: Implementing authenticated Smart HTTP - which URLs to secure

[Shawn Pearce <spearce@spearce.org>]

On Sun, Jul 15, 2012 at 6:43 AM, Jonas H. <jonas@lophus.org> wrote:
> I'd like to implement HTTP authentication for Git Smart HTTP using Dulwich
> (a Python binding):
>
> 1) read-only if unauthenticated and write only if authenticated
> 2) read/write only if authenticated
>
> I couldn't find any documentation on which URLs need be secured and what
> response codes are expected in case the cloner/pusher is unauthenticated.

Smart HTTP uses HTTP authentication, so return 401 with a proper
WWW-Authenticate header to prompt the client for authentication, and
use the Authorization header to verify the client. Return 403 to tell
the client they cannot access the service because the Authorization
header is invalid[1].

You can tell check for a write request by looking at the service
parameter on the /info/refs request, if its git-receive-pack, you are
about to receive a write, so you want to prompt for authentication.
You should also check for authentication on the /git-receive-pack
request.

[1] This is actually a lie. The servers I have written over the years
return 200 OK with a special Git payload in this case. The payload
uses the "ERR" in the /info/refs response to print a message to the
client telling the user access is forbidden. This allows a custom
message to be sent, and stops the client from discarding the message
and falling back to the dumb protocol.

> Is there any documentation on Smart HTTP workflow?  The C sources (vanilla
> Git and libgit2) didn't help me too much since I found it very difficult to
> follow the code-flow... it's probably just abstracted too well :-)

There is no authentication/authorization in the server components in
git-core. This is delegated to the web server that runs in front of
Git, just like with the system SSH server handling authentication for
Git over SSH.