http: preserve wwwauth_headers across redirects

When cURL follows a redirect, it calls the CURLOPT_HEADERFUNCTION for
each header received including ones from a redirect. http_request() sets
fwrite_wwwauth() as the header function, which will record the wwwauth[]
entries for the last step in the redirection chain.

However, when http_request_recoverable() sees that cURL followed a
redirect, it attempts to update the credentials for the request from the
new URL using credential_from_url(). The first thing that does is call
credential_clear(), which clears everything including wwwauth_headers.

If the new URL should use a credential helper rather than credentials
embedded in the URL, this loses the list of authentication methods that
the server provided in the redirect.

For example, I have a server that supports HTTP but always redirects to
HTTPS before handling requests. This redirect breaks OAuth
authentication:

  $ git ls-remote http://server/git
  => Send header: GET /git/info/refs?service=git-upload-pack HTTP/1.1
  <= Recv header: HTTP/1.1 302 Found
  <= Recv header: Location: https://server.nvidia.com/git/info/refs?service=git-upload-pack
  == Info: Issue another request to this URL: 'https://server.nvidia.com/git/info/refs?service=git-upload-pack'
  => Send header: GET /git/info/refs?service=git-upload-pack HTTP/1.1
  <= Recv header: HTTP/1.1 401 Unauthorized
  <= Recv header: WWW-Authenticate: Bearer error="invalid_request", error_description="No bearer token found in the request", msal-tenant-id="<tenant>", msal-client-id="<client>"
  trace: run_command: 'git credential-cache --timeout 7200 get'
  trace: start_command: /bin/sh -c 'git credential-cache --timeout 7200 get' 'git credential-cache --timeout 7200 get'
  trace: built-in: git credential-cache --timeout 7200 get
  trace: run_command: 'git credential-msal get'
  trace: start_command: /bin/sh -c 'git credential-msal get' 'git credential-msal get'
  trace: exec: git-credential-msal get
  trace: run_command: git-credential-msal get
  trace: start_command: /usr/bin/git-credential-msal get
  Username for 'https://server.nvidia.com': ^C

When git invokes the credential helper, it doesn't include the wwwauth[]
array, so git-credential-msal doesn't think that OAuth is supported [1].

Fix the problem by preserving the wwwauth_headers strvec across the call
to credential_from_url().

[1] https://github.com/Binary-Eater/git-credential-msal/blob/trunk/src/git_credential_msal/main.py#L69

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http.c

@@ -2354,7 +2354,21 @@ static int http_request_recoverable(const char *url,
 	if (options->effective_url && options->base_url) {
 		if (update_url_from_redirect(options->base_url,
 					     url, options->effective_url)) {
+			struct strvec wwwauth_headers = STRVEC_INIT;
+
+			/*
+			 * Preserve wwwauth_headers across the call to
+			 * credential_from_url(): if the effective URL doesn't
+			 * specify its own credentials, a credential helper
+			 * might need the wwwauth[] array from the server's
+			 * redirect response in order to authenticate.
+			 */
+			strvec_pushv(&wwwauth_headers,
+				     http_auth.wwwauth_headers.v);
 			credential_from_url(&http_auth, options->base_url->buf);
+			strvec_pushv(&http_auth.wwwauth_headers,
+				     wwwauth_headers.v);
+			strvec_clear(&wwwauth_headers);
 			url = options->effective_url->buf;
 		}
 	}

t/lib-httpd/apache.conf

@@ -202,6 +202,7 @@ RewriteRule ^/dumb-redir/(.*)$ /dumb/$1 [R=301]
 RewriteRule ^/smart-redir-perm/(.*)$ /smart/$1 [R=301]
 RewriteRule ^/smart-redir-temp/(.*)$ /smart/$1 [R=302]
 RewriteRule ^/smart-redir-auth/(.*)$ /auth/smart/$1 [R=301]
+RewriteRule ^/custom_auth_redir/(.*)$ /custom_auth/$1 [R=302]
 RewriteRule ^/smart-redir-limited/(.*)/info/refs$ /smart/$1/info/refs [R=301]
 RewriteRule ^/ftp-redir/(.*)$ ftp://localhost:1000/$1 [R=302]
 

t/t5563-simple-http-auth.sh

@@ -557,6 +557,51 @@ test_expect_success 'access using bearer auth' '
 	EOF
 '
 
+test_expect_success 'bearer auth after redirect preserves wwwauth headers' '
+	test_when_finished "per_test_cleanup" &&
+
+	set_credential_reply get <<-EOF &&
+	capability[]=authtype
+	authtype=Bearer
+	credential=YS1naXQtdG9rZW4=
+	EOF
+
+	cat >"$HTTPD_ROOT_PATH/custom-auth.valid" <<-EOF &&
+	id=1 creds=Bearer YS1naXQtdG9rZW4=
+	EOF
+
+	cat >"$HTTPD_ROOT_PATH/custom-auth.challenge" <<-EOF &&
+	id=1 status=200
+	id=default response=WWW-Authenticate: FooBar param1="value1" param2="value2"
+	id=default response=WWW-Authenticate: Bearer authorize_uri="id.example.com" p=1 q=0
+	id=default response=WWW-Authenticate: Basic realm="example.com"
+	EOF
+
+	test_config_global credential.helper test-helper &&
+	test_config_global credential.useHttpPath true &&
+	git ls-remote "$HTTPD_URL/custom_auth_redir/repo.git" &&
+
+	expect_credential_query get <<-EOF &&
+	capability[]=authtype
+	capability[]=state
+	protocol=http
+	host=$HTTPD_DEST
+	path=custom_auth/repo.git
+	wwwauth[]=FooBar param1="value1" param2="value2"
+	wwwauth[]=Bearer authorize_uri="id.example.com" p=1 q=0
+	wwwauth[]=Basic realm="example.com"
+	EOF
+
+	expect_credential_query store <<-EOF
+	capability[]=authtype
+	authtype=Bearer
+	credential=YS1naXQtdG9rZW4=
+	protocol=http
+	host=$HTTPD_DEST
+	path=custom_auth/repo.git
+	EOF
+'
+
 test_expect_success 'access using bearer auth with invalid credentials' '
 	test_when_finished "per_test_cleanup" &&