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Re: [RFC PATCH v1] http: add http.keepRejectedCredentials config




Why must the credentials must be deleted after receiving the 401 (or
any) error? What's the rationale for this?

On Mon, Jun 4, 2018 at 10:47 AM, Jeff King <peff@xxxxxxxx> wrote:
> On Mon, Jun 04, 2018 at 05:26:35AM -0700, lars.schneider@xxxxxxxxxxxx wrote:
>
>> From: Lars Schneider <larsxschneider@xxxxxxxxx>
>>
>> If a Git HTTP server responds with 401 or 407, then Git tells the
>> credential helper to reject and delete the credentials. In general
>> this is good.
>>
>> However, in certain automation environments it is not desired to remove
>> credentials automatically. This is in particular the case if credentials
>> are only invalid temporarily (e.g. because of problems in the server's
>> authentication backend).
>>
>> Therefore, add the config "http.keepRejectedCredentials" which tells
>> Git to keep invalid credentials if set to "true".
>
> It seems like those servers should be returning a value besides "401" if
> it's a temporary error.
>
> But alas, we live in the real world, and your patch seems like a pretty
> sensible workaround for clients. This could be done at the helper layer,
> but I think in practice doing it here is going to be a lot more
> convenient (and doesn't preclude helpers having their own logic if
> people care to extend them in that direction).
>
>> It was considered to disable the credential deletion in credential.c
>> directly. This approach was not chosen as it could be confusing to
>> other callers of credential_reject() if the function does not do what
>> its name says (e.g. in imap-send.c).
>
> Yeah, I think "git credential" relies on that code, too, and you
> probably should be able to manually forget a credential at that plumbing
> layer.
>
>> diff --git a/Documentation/config.txt b/Documentation/config.txt
>> index ab641bf5a9..184aee8dbc 100644
>> --- a/Documentation/config.txt
>> +++ b/Documentation/config.txt
>> @@ -1997,6 +1997,12 @@ http.emptyAuth::
>>       a username in the URL, as libcurl normally requires a username for
>>       authentication.
>>
>> +http.keepRejectedCredentials::
>> +     Keep credentials in the credential helper that a Git server responded
>> +     to with 401 (unauthorized) or 407 (proxy authentication required).
>> +     This can be useful in automation environments where credentials might
>> +     become temporarily invalid. The default is `false`.
>
> Looks good.
>
>>  http.delegation::
>>       Control GSSAPI credential delegation. The delegation is disabled
>>       by default in libcurl since version 7.21.7. Set parameter to tell
>> diff --git a/http.c b/http.c
>> index b4bfbceaeb..ff6932813f 100644
>> --- a/http.c
>> +++ b/http.c
>> @@ -138,6 +138,7 @@ static int ssl_cert_password_required;
>>  #ifdef LIBCURL_CAN_HANDLE_AUTH_ANY
>>  static unsigned long http_auth_methods = CURLAUTH_ANY;
>>  static int http_auth_methods_restricted;
>> +static int keep_rejected_credentials = 0;
>
> Minor nit, but we usually skip the redundant "= 0" for BSS variables.
>
>> @@ -403,6 +404,11 @@ static int http_options(const char *var, const char *value, void *cb)
>>               return 0;
>>       }
>>
>> +     if (!strcmp("http.keeprejectedcredentials", var)) {
>> +             keep_rejected_credentials = git_config_bool(var, value);
>> +             return 0;
>> +     }
>> +
>>       /* Fall back on the default ones */
>>       return git_default_config(var, value, cb);
>>  }
>> @@ -1471,7 +1477,8 @@ static int handle_curl_result(struct slot_results *results)
>>               return HTTP_MISSING_TARGET;
>>       else if (results->http_code == 401) {
>>               if (http_auth.username && http_auth.password) {
>> -                     credential_reject(&http_auth);
>> +                     if (!keep_rejected_credentials)
>> +                             credential_reject(&http_auth);
>
> The rest of the patch looks good.
>
> It's possible we'd eventually want a similar feature for other
> protocols, like IMAP. And that we'd in the long run prefer to have a
> single credential.keepRejected that covers them all. Or maybe not. Given
> that this is kind of a workaround, people might ultimately want
> protocol-specific options. So I'm happy to start with "http" for now and
> deal with other protocols down the road (if it's even necessary).
>
> Some scripts that use "git credential" may want to support this config
> option, too (I'm thinking of git-remote-mediawiki, which I believe
> uses it for http requests). But those can be added one by one to the
> porcelain scripts.
>
> So modulo the minor "= 0" nit, this all looks good to me.
>
> -Peff