[FEATURE] Add CSP middleware

lib/middleware/csp.js

@@ -0,0 +1,69 @@
+const url = require("url");
+const querystring = require("querystring");
+
+const HEADER_CONTENT_SECURITY_POLICY = "Content-Security-Policy";
+const HEADER_CONTENT_SECURITY_POLICY_REPORT_ONLY = "Content-Security-Policy-Report-Only";
+const rPolicy = /([-_a-zA-Z0-9]+)(:report-only)?/i;
+
+function createMiddleware(sCspUrlParameterName, oConfig) {
+	const {
+		allowDynamicPolicySelection=false,
+		allowDynamicPolicyDefinition=false,
+		defaultPolicyIsReportOnly=false
+	} = oConfig;
+
+	return function csp(req, res, next) {
+		let oPolicy;
+		let bReportOnly = defaultPolicyIsReportOnly;
+
+		// If a policy with name 'default' is defined, it will even be send without a present URL parameter.
+		if (oConfig.definedPolicies["default"]) {
+			oPolicy = {
+				name: "default",
+				policy: oConfig.definedPolicies["default"]
+			};
+		}
+
+		// Use random protocol, host and port to establish a valid URL for parsing query parameters
+		let oParsedUrl = url.parse(req.url);
+		let oQuery = querystring.parse(oParsedUrl.query);
+		let sCspUrlParameterValue = oQuery[sCspUrlParameterName];
+
+		if (sCspUrlParameterValue) {
+			let mPolicyMatch = rPolicy.exec(sCspUrlParameterValue);
+
+			if (mPolicyMatch && mPolicyMatch[1]
+				&& oConfig.definedPolicies[mPolicyMatch[1]] && allowDynamicPolicySelection) {
+				oPolicy = {
+					name: mPolicyMatch[1],
+					policy: oConfig.definedPolicies[mPolicyMatch[1]]
+				};
+				bReportOnly = mPolicyMatch[2] !== undefined;
+			} else if (allowDynamicPolicyDefinition) {
+				// Custom CSP policy directives get passed as part of the CSP URL-Parameter value
+				bReportOnly = sCspUrlParameterValue.endsWith(":report-only");
+				if (bReportOnly) {
+					sCspUrlParameterValue = sCspUrlParameterValue.slice(0, - ":report-only".length);
+				}
+				oPolicy = {
+					name: "dynamic-custom-policy",
+					policy: sCspUrlParameterValue
+				};
+			}
+		}
+
+		if (oPolicy) {
+			let sHeader = bReportOnly ? HEADER_CONTENT_SECURITY_POLICY_REPORT_ONLY : HEADER_CONTENT_SECURITY_POLICY;
+			let sHeaderValue = oPolicy.policy;
+
+			// Send response with CSP header
+			res.removeHeader(HEADER_CONTENT_SECURITY_POLICY);
+			res.removeHeader(HEADER_CONTENT_SECURITY_POLICY_REPORT_ONLY);
+			res.setHeader(sHeader, sHeaderValue);
+		}
+
+		next();
+	};
+}
+
+module.exports = createMiddleware;

lib/server.js

@@ -8,6 +8,7 @@ const serveResources = require("./middleware/serveResources");
 const discovery = require("./middleware/discovery");
 const versionInfo = require("./middleware/versionInfo");
 const serveThemes = require("./middleware/serveThemes");
+const csp = require("./middleware/csp");
 const ui5connect = require("connect-openui5");
 const nonReadRequests = require("./middleware/nonReadRequests");
 const ui5Fs = require("@ui5/fs");
@@ -50,6 +51,34 @@ function serve(tree, {port, changePortIfInUse = false, h2 = false, key, cert, ac
 		};
 
 		const app = express();
+
+		const oCspConfig = {
+			allowDynamicPolicySelection: true,
+			allowDynamicPolicyDefinition: true,
+			defaultPolicyIsReportOnly: true,
+			definedPolicies: {
+				"sap-target-level-1":
+					"default-src 'self'; " +
+					"script-src  'self' 'unsafe-eval'; " +
+					"style-src   'self' 'unsafe-inline'; " +
+					"font-src    'self' data:; " +
+					"img-src     'self' * data: blob:; " +
+					"frame-src   'self' https: data: blob:; " +
+					"child-src   'self' https: data: blob:; " +
+					"connect-src 'self' https: wss:;",
+				"sap-target-level-2":
+					"default-src 'self'; " +
+					"script-src  'self'; " +
+					"style-src   'self' 'unsafe-inline'; " +
+					"font-src    'self' data:; " +
+					"img-src     'self' * data: blob:; " +
+					"frame-src   'self' https: data: blob:; " +
+					"child-src   'self' https: data: blob:; " +
+					"connect-src 'self' https: wss:;"
+			}
+		};
+		app.use(csp("sap-ui-xx-csp-policy", oCspConfig));
+
 		app.use(compression());
 		app.use(cors());
 

test/lib/server.js

@@ -379,3 +379,50 @@ test("Start server twice - Port is already taken and the next one is used", (t)
 		t.fail(error);
 	});
 });
+
+test("CSP", (t) => {
+	return Promise.all([
+		request.get("/index.html?sap-ui-xx-csp-policy=sap-target-level-1").then((res) => {
+			t.truthy(res.headers["content-security-policy"], "response should have csp header");
+			t.regex(res.headers["content-security-policy"], /script-src\s+'self'\s+'unsafe-eval'\s*;/,
+				"policy should should have the expected content");
+			t.is(res.headers["content-security-policy-report-only"], undefined,
+				"response must not have csp report-only header");
+		}),
+		request.get("/index.html?sap-ui-xx-csp-policy=sap-target-level-1:report-only").then((res) => {
+			t.is(res.headers["content-security-policy"], undefined, "response must not have csp header");
+			t.truthy(res.headers["content-security-policy-report-only"],
+				"response should have report-only csp header");
+			t.regex(res.headers["content-security-policy-report-only"], /script-src\s+'self'\s+'unsafe-eval'\s*;/,
+				"policy should should have the expected content");
+		}),
+		request.get("/index.html?sap-ui-xx-csp-policy=sap-target-level-2").then((res) => {
+			t.truthy(res.headers["content-security-policy"], "response should have csp header");
+			t.regex(res.headers["content-security-policy"], /script-src\s+'self'\s*;/,
+				"policy should should have the expected content");
+			t.is(res.headers["content-security-policy-report-only"], undefined,
+				"response must not have csp report-only header");
+		}),
+		request.get("/index.html?sap-ui-xx-csp-policy=sap-target-level-2:report-only").then((res) => {
+			t.is(res.headers["content-security-policy"], undefined, "response must not have csp header");
+			t.truthy(res.headers["content-security-policy-report-only"],
+				"response should have report-only csp header");
+			t.regex(res.headers["content-security-policy-report-only"], /script-src\s+'self'\s*;/,
+				"policy should should have the expected content");
+		}),
+		request.get("/index.html?sap-ui-xx-csp-policy=default-src%20'self';").then((res) => {
+			t.truthy(res.headers["content-security-policy"], "response should have csp header");
+			t.regex(res.headers["content-security-policy"], /default-src\s+'self'\s*;/,
+				"policy should should have the expected content");
+			t.is(res.headers["content-security-policy-report-only"], undefined,
+				"response must not have csp report-only header");
+		}),
+		request.get("/index.html?sap-ui-xx-csp-policy=default-src%20'self';:report-only").then((res) => {
+			t.is(res.headers["content-security-policy"], undefined, "response must not have csp header");
+			t.truthy(res.headers["content-security-policy-report-only"],
+				"response should have report-only csp header");
+			t.regex(res.headers["content-security-policy-report-only"], /default-src\s+'self'\s*;/,
+				"policy should should have the expected content");
+		})
+	]);
+});