[PATCH] credential: clear expired c->credential in addition to c->password

[Aaron Plattner <aplattner@nvidia.com>]

When a struct credential expires, credential_fill() clears c->password
so that clients don't try to use it later. However, a struct cred that
uses an alternate authtype won't have a password, but might have a
credential stored in c->credential. Clear that too.

This is a problem, for example, when an OAuth2 bearer token is used. In
the system I'm using, the OAuth2 configuration generates and caches a
bearer token that is valid for an hour. After the token expires, git
needs to call back into the credential helper to use a stored refresh
token to get a new bearer token. But if c->credential is still non-NULL,
git will instead try to use the expired token and fail with an error:

 fatal: Authentication failed for 'https://<oauth2-enabled-server>/repository'

And on the server:

 [auth_openidc:error] [client <ip>:34012] oidc_proto_validate_exp: "exp" validation failure (1717522989): JWT expired 224 seconds ago

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
---
 credential.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/credential.c b/credential.c
index 758528b291..38b51e11cb 100644
--- a/credential.c
+++ b/credential.c
@@ -480,8 +480,9 @@ void credential_fill(struct credential *c, int all_capabilities)
 	for (i = 0; i < c->helpers.nr; i++) {
 		credential_do(c, c->helpers.items[i].string, "get");
 		if (c->password_expiry_utc < time(NULL)) {
-			/* Discard expired password */
+			/* Discard expired credentials */
 			FREE_AND_NULL(c->password);
+			FREE_AND_NULL(c->credential);
 			/* Reset expiry to maintain consistency */
 			c->password_expiry_utc = TIME_MAX;
 		}
-- 
2.45.2.409.g7b0defb391