reverse-proxy: T6370: Set custom HTTP headers in reverse-proxy responses (backport #3487)

data/templates/load-balancing/haproxy.cfg.j2

@@ -81,6 +81,11 @@ frontend {{ front }}
 {%                     endif %}
 {%                 endfor %}
 {%             endif %}
+{%             if front_config.http_response_headers is vyos_defined %}
+{%                 for header, header_config in front_config.http_response_headers.items() %}
+    http-response set-header {{ header }} '{{ header_config['value'] }}'
+{%                 endfor %}
+{%             endif %}
 {%         endif %}
 {%         if front_config.rule is vyos_defined %}
 {%             for rule, rule_config in front_config.rule.items() %}
@@ -158,6 +163,11 @@ backend {{ back }}
 {%         endif %}
 {%         if back_config.mode is vyos_defined %}
     mode {{ back_config.mode }}
+{%             if back_config.http_response_headers is vyos_defined %}
+{%                 for header, header_config in back_config.http_response_headers.items() %}
+    http-response set-header {{ header }} '{{ header_config['value'] }}'
+{%                 endfor %}
+{%             endif %}
 {%         endif %}
 {%         if back_config.rule is vyos_defined %}
 {%             for rule, rule_config in back_config.rule.items() %}

interface-definitions/include/haproxy/http-response-headers.xml.i

@@ -0,0 +1,29 @@
+<!-- include start from haproxy/http-response-headers.xml.i -->
+<tagNode name="http-response-headers">
+  <properties>
+    <help>Headers to include in HTTP response</help>
+    <valueHelp>
+      <format>txt</format>
+      <description>HTTP header name</description>
+    </valueHelp>
+    <constraint>
+      <regex>[-a-zA-Z]+</regex>
+    </constraint>
+    <constraintErrorMessage>Header names must only include alphabetical characters and hyphens</constraintErrorMessage>
+  </properties>
+  <children>
+    <leafNode name="value">
+      <properties>
+        <help>HTTP header value</help>
+        <valueHelp>
+          <format>txt</format>
+          <description>HTTP header value</description>
+        </valueHelp>
+        <constraint>
+          <regex>[[:ascii:]]{1,256}</regex>
+        </constraint>
+      </properties>
+    </leafNode>
+  </children>
+</tagNode>
+<!-- include end -->

interface-definitions/load-balancing_reverse-proxy.xml.in

@@ -39,6 +39,7 @@
               #include <include/port-number.xml.i>
               #include <include/haproxy/rule-frontend.xml.i>
               #include <include/haproxy/tcp-request.xml.i>
+              #include <include/haproxy/http-response-headers.xml.i>
               <leafNode name="redirect-http-to-https">
                 <properties>
                   <help>Redirect HTTP to HTTPS</help>
@@ -90,6 +91,7 @@
               </leafNode>
               #include <include/generic-description.xml.i>
               #include <include/haproxy/mode.xml.i>
+              #include <include/haproxy/http-response-headers.xml.i>
               <node name="parameters">
                 <properties>
                   <help>Backend parameters</help>

smoketest/scripts/cli/test_load-balancing_reverse-proxy.py

@@ -385,5 +385,26 @@ def test_06_lb_reverse_proxy_tcp_mode(self):
         self.assertIn(f'mode {mode}', config)
         self.assertIn(f'server {bk_name} {bk_server}:{bk_server_port}', config)
 
+    def test_07_lb_reverse_proxy_http_response_headers(self):
+        # Setup base
+        self.configure_pki()
+        self.base_config()
+
+        # Set example headers in both frontend and backend
+        self.cli_set(base_path + ['service', 'https_front', 'http-response-headers', 'Cache-Control', 'value', 'max-age=604800'])
+        self.cli_set(base_path + ['backend', 'bk-01',  'http-response-headers', 'Proxy-Backend-ID', 'value', 'bk-01'])
+        self.cli_commit()
+
+        # Test headers are present in generated configuration file
+        config = read_file(HAPROXY_CONF)
+        self.assertIn('http-response set-header Cache-Control \'max-age=604800\'', config)
+        self.assertIn('http-response set-header Proxy-Backend-ID \'bk-01\'', config)
+
+        # Test setting alongside modes other than http is blocked by validation conditions
+        self.cli_set(base_path + ['service', 'https_front', 'mode', 'tcp'])
+        with self.assertRaises(ConfigSessionError) as e:
+            self.cli_commit()
+
+
 if __name__ == '__main__':
     unittest.main(verbosity=2)

src/conf_mode/load-balancing_reverse-proxy.py

@@ -88,6 +88,12 @@ def verify(lb):
             if {'send_proxy', 'send_proxy_v2'} <= set(bk_server_conf):
                 raise ConfigError(f'Cannot use both "send-proxy" and "send-proxy-v2" for server "{bk_server}"')
 
+    # Check if http-response-headers are configured in any frontend/backend where mode != http
+    for group in ['service', 'backend']:
+        for config_name, config in lb[group].items():
+            if 'http_response_headers' in config and ('mode' not in config or config['mode'] != 'http'):
+                raise ConfigError(f'{group} {config_name} must be set to http mode to use http_response_headers!')
+
         if 'ssl' in back_config:
             if {'no_verify', 'ca_certificate'} <= set(back_config['ssl']):
                 raise ConfigError(f'backend {back} cannot have both ssl options no-verify and ca-certificate set!')