threads / discuss / 31030

Implementing authenticated Smart HTTP - which URLs to secure

Subject: Implementing authenticated Smart HTTP - which URLs to secure

## tl;dr

3 messages between Jul 15, 2012 and Jul 16, 2012.

replies: 2people: 2as markdown or json

Jonas H.· Jul 15, 2012, 13:43 UTC · lore

Howdy!

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.

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 :-)

Thanks! Jonas

Shawn Pearce· Jul 15, 2012, 20:49 UTC · re: Jonas H. · lore

Re: Implementing authenticated Smart HTTP - which URLs to secure

On Sun, Jul 15, 2012 at 6:43 AM, Jonas H. <jonas@lophus.org> wrote:

Show 8 quoted lines

> 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.

Jonas H.· Jul 16, 2012, 17:36 UTC · re: Shawn Pearce · lore

Re: Implementing authenticated Smart HTTP - which URLs to secure

On 07/15/2012 10:49 PM, Shawn Pearce wrote:

Show 21 quoted lines

> 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.

Thanks man! That helped a lot. I figured it has something to do with the argument to /info/refs but didn't make the connection between "I want to upload" and "git-receive-pack" -- it's pretty confusing that the argument is "receive" if I want to *upload*. At least when you don't know the argument is the name of the service the client wants the server to start.

Show 6 quoted lines

> [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.

I just experienced that exact problem. What worked for me is just keeping responding with 401 Unauthorized. Git will give up with a nice error message ("Authentication failed") after a 2 or so tries.

Do you know of any better way that does not require using the raw Git protocol?

> 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.

Well that explains why I couldn't find anything helpful in the code :-) Though I'm a bit confused by the lack of documentation on the subject since I'm probably not the first one to set up a Git server with authentication?!

Jonas