[PATCH v2 01/16] credential: add an authtype field

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Apr 17, 2024, 00:02 UTC
Message-ID: <20240417000240.3611948-2-sandals@crustytoothpaste.net>
In-Reply-To: <20240417000240.3611948-1-sandals@crustytoothpaste.net>

When Git makes an HTTP request, it can negotiate the type of authentication to use with the server provided the authentication scheme is one of a few well-known types (Basic, Digest, NTLM, or Negotiate). However, some servers wish to use other types of authentication, such as the Bearer type from OAuth2. Since libcurl doesn't natively support this type, it isn't possible to use it, and the user is forced to specify the Authorization header using the http.extraheader setting.

However, storing a plaintext token in the repository configuration is not very secure, especially if a repository can be shared by multiple parties. We already have support for many types of secure credential storage by using credential helpers, so let's teach credential helpers how to produce credentials for an arbitrary scheme.

If the credential helper specifies an authtype field, then it specifies an authentication scheme (e.g., Bearer) and the password field specifies the raw authentication token, with any encoding already specified. We reuse the password field for this because some credential helpers store the metadata without encryption even though the password is encrypted, and we'd like to avoid insecure storage if an older version of the credential helper gets ahold of the data.

The username is not used in this case, but it is still preserved for the purpose of finding the right credential if the user has multiple accounts.

If the authtype field is not specified, then the password behaves as normal and it is passed along with the username to libcurl.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 credential.c | 5 +++++
 credential.h | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/credential.c b/credential.c
index 18098bd35e..3dec433df5 100644
--- a/credential.c
+++ b/credential.c
@@ -26,6 +26,7 @@ void credential_clear(struct credential *c)
 	free(c->username);
 	free(c->password);
 	free(c->oauth_refresh_token);
+	free(c->authtype);
 	string_list_clear(&c->helpers, 0);
 	strvec_clear(&c->wwwauth_headers);
 
@@ -252,6 +253,9 @@ int credential_read(struct credential *c, FILE *fp)
 		} else if (!strcmp(key, "oauth_refresh_token")) {
 			free(c->oauth_refresh_token);
 			c->oauth_refresh_token = xstrdup(value);
+		} else if (!strcmp(key, "authtype")) {
+			free(c->authtype);
+			c->authtype = xstrdup(value);
 		} else if (!strcmp(key, "url")) {
 			credential_from_url(c, value);
 		} else if (!strcmp(key, "quit")) {
@@ -295,6 +299,7 @@ void credential_write(const struct credential *c, FILE *fp)
 	}
 	for (size_t i = 0; i < c->wwwauth_headers.nr; i++)
 		credential_write_item(fp, "wwwauth[]", c->wwwauth_headers.v[i], 0);
+	credential_write_item(fp, "authtype", c->authtype, 0);
 }
 
 static int run_credential_helper(struct credential *c,
diff --git a/credential.h b/credential.h
index acc41adf54..dc96ca0318 100644
--- a/credential.h
+++ b/credential.h
@@ -143,6 +143,12 @@ struct credential {
 	char *path;
 	char *oauth_refresh_token;
 	timestamp_t password_expiry_utc;
+
+	/**
+	 * The authorization scheme to use.  If this is NULL, libcurl is free to
+	 * negotiate any scheme it likes.
+	 */
+	char *authtype;
 };
 
 #define CREDENTIAL_INIT { \