add intercept tests

Signed-off-by: Mohammed Al Sahaf <msaa1990@gmail.com>

caddytest/spec/http/intercept/spec.hurl

@@ -0,0 +1,129 @@
+# Configure Caddy with intercept copying headers
+POST http://localhost:2019/load
+Content-Type: text/caddyfile
+```
+{
+	skip_install_trust
+	http_port     9080
+	https_port    9443
+	local_certs
+}
+localhost {
+	intercept {
+		@all status 2xx
+		handle_response @all {
+			header X-Intercepted "yes"
+		}
+	}
+	respond "Original"
+}
+```
+
+# intercept can add headers while passing the original body through
+GET https://localhost:9443
+[Options]
+insecure: true
+HTTP 200
+[Asserts]
+header "X-Intercepted" == "yes"
+body == "Original"
+
+
+# Configure Caddy with intercept replacing content
+POST http://localhost:2019/load
+Content-Type: text/caddyfile
+```
+{
+	skip_install_trust
+	http_port     9080
+	https_port    9443
+	local_certs
+}
+localhost {
+	intercept {
+		@all status 2xx
+		handle_response @all {
+			respond "Intercepted response"
+		}
+	}
+	respond "Original"
+}
+```
+
+# intercept can completely replace response
+GET https://localhost:9443
+[Options]
+insecure: true
+HTTP 200
+[Asserts]
+body == "Intercepted response"
+
+
+# Configure Caddy with replace_status using an inline status code
+# NOTE: the next two scenarios document the intended behavior of replace_status
+# and currently fail due to an upstream bug in intercept's WriteHeader receiver.
+# Fixed in #7810
+POST http://localhost:2019/load
+Content-Type: text/caddyfile
+```
+{
+	skip_install_trust
+	http_port     9080
+	https_port    9443
+	local_certs
+}
+localhost {
+	intercept {
+		replace_status 404
+	}
+	respond "Original" 200
+}
+```
+
+# replace_status overrides the upstream status code while passing the body through
+GET https://localhost:9443/
+[Options]
+insecure: true
+HTTP 404
+[Asserts]
+body == "Original"
+
+
+# Configure Caddy with replace_status using a named response matcher
+POST http://localhost:2019/load
+Content-Type: text/caddyfile
+```
+{
+	skip_install_trust
+	http_port     9080
+	https_port    9443
+	local_certs
+}
+localhost {
+	intercept {
+		@server_error status 5xx
+		replace_status @server_error 503
+	}
+	route /boom {
+		respond "kaboom" 500
+	}
+	respond "ok" 200
+}
+```
+
+# replace_status rewrites the status only when the matcher matches
+GET https://localhost:9443/boom
+[Options]
+insecure: true
+HTTP 503
+[Asserts]
+body == "kaboom"
+
+
+# unmatched responses are passed through unchanged
+GET https://localhost:9443/healthy
+[Options]
+insecure: true
+HTTP 200
+[Asserts]
+body == "ok"