chore: implement microsoft key caching to combat rate limiting

src/common/Logger.ts

@@ -42,3 +42,32 @@ export const writeLogMessage = (event: APIGatewayTokenAuthorizerEvent, log: ILog
   }
   return log;
 };
+
+export enum LogLevel {
+  DEBUG = "DEBUG",
+  INFO = "INFO",
+  WARN = "WARN",
+  ERROR = "ERROR",
+}
+
+export const envLogger = (level: LogLevel, ...messages: string[]) => {
+  if (process.env.DEBUG === "true") {
+    switch (level) {
+      case LogLevel.DEBUG:
+        console.debug(messages);
+        break;
+      case LogLevel.INFO:
+        console.info(messages);
+        break;
+      case LogLevel.WARN:
+        console.warn(messages);
+        break;
+      case LogLevel.ERROR:
+        console.error(messages);
+        break;
+      default:
+        console.log(messages);
+        return;
+    }
+  }
+};

src/functions/authorizer.ts

@@ -6,7 +6,7 @@ import { generatePolicy as generateFunctionalPolicy } from "./functionalPolicyFa
 import { getValidJwt } from "../services/tokens";
 import { JWT_MESSAGE } from "../models/enums";
 import { ILogEvent } from "../models/ILogEvent";
-import { writeLogMessage } from "../common/Logger";
+import { envLogger, LogLevel, writeLogMessage } from "../common/Logger";
 import newPolicyDocument from "./newPolicyDocument";
 import { Jwt, JwtPayload } from "jsonwebtoken";
 
@@ -20,25 +20,35 @@ import { Jwt, JwtPayload } from "jsonwebtoken";
 export const authorizer = async (event: APIGatewayTokenAuthorizerEvent, context: Context): Promise<APIGatewayAuthorizerResult> => {
   const logEvent: ILogEvent = {};
 
+  envLogger(LogLevel.DEBUG, "Invoked authoriser");
+
   if (!process.env.AZURE_TENANT_ID || !process.env.AZURE_CLIENT_ID) {
     writeLogMessage(event, logEvent, JWT_MESSAGE.INVALID_ID_SETUP);
     return unauthorisedPolicy();
   }
 
+  envLogger(LogLevel.DEBUG, "AZURE_TENANT_ID and AZURE_CLIENT_ID are set");
+
   try {
     initialiseLogEvent(event);
+
+    envLogger(LogLevel.INFO, "Getting valid JWT");
     const jwt = await getValidJwt(event.authorizationToken, logEvent, process.env.AZURE_TENANT_ID, process.env.AZURE_CLIENT_ID);
 
+    envLogger(LogLevel.INFO, "Generating role policy");
     const policy = generateRolePolicy(jwt, logEvent) ?? generateFunctionalPolicy(jwt, logEvent);
 
     if (policy !== undefined) {
+      envLogger(LogLevel.INFO, "Role policy generated");
       return policy;
     }
 
     reportNoValidRoles(jwt, event, context, logEvent);
     writeLogMessage(event, logEvent, JWT_MESSAGE.INVALID_ROLES);
+
     return unauthorisedPolicy();
   } catch (error: any) {
+    envLogger(LogLevel.ERROR, "Catch - Error occurred", error);
     writeLogMessage(event, logEvent, error);
     return unauthorisedPolicy();
   }
@@ -67,6 +77,8 @@ const reportNoValidRoles = (jwt: Jwt, event: APIGatewayTokenAuthorizerEvent, con
  * @param event
  */
 const initialiseLogEvent = (event: APIGatewayTokenAuthorizerEvent): ILogEvent => {
+  envLogger(LogLevel.DEBUG, "Init log event");
+
   return {
     requestUrl: event.methodArn,
     timeOfRequest: new Date().toISOString(),

src/services/azure.ts

@@ -1,7 +1,20 @@
 import { KeyResponse } from "../models/KeyResponse";
+import { envLogger, LogLevel } from "../common/Logger";
+
+const cache: Map<string, Map<string, string>> = new Map();
 
 export const getCertificateChain = async (tenantId: string, keyId: string): Promise<string> => {
-  const keys: Map<string, string> = await getKeys(tenantId);
+  const cacheKeys = cache.get(tenantId);
+
+  envLogger(LogLevel.DEBUG, `Cache ${cacheKeys ? "hit" : "not hit"}`);
+
+  const keys: Map<string, string> = cacheKeys ?? (await getKeys(tenantId));
+
+  envLogger(LogLevel.DEBUG, "Public keys read");
+
+  if (!cache.has(tenantId)) {
+    cache.set(tenantId, keys);
+  }
 
   const certificateChain = keys.get(keyId);
 
@@ -25,9 +38,12 @@ const getKeys = async (tenantId: string): Promise<Map<string, string>> => {
 
     map.set(keyId, certificateChain);
   }
+
+  envLogger(LogLevel.DEBUG, "Key Map Created");
   return map;
 };
 
 export const fetchKeys = (tenantId: string) => {
+  envLogger(LogLevel.DEBUG, `Fetching keys from https://login.microsoftonline.com/${tenantId}/discovery/keys`);
   return fetch(`https://login.microsoftonline.com/${tenantId}/discovery/keys`);
 };

src/services/signature-check.ts

@@ -1,10 +1,13 @@
 import * as JWT from "jsonwebtoken";
 import { getCertificateChain } from "./azure";
+import { envLogger, LogLevel } from "../common/Logger";
 
 export const checkSignature = async (encodedToken: string, decodedToken: JWT.Jwt, tenantId: string, clientId: string): Promise<void> => {
   // tid = tenant ID, kid = key ID
+  envLogger(LogLevel.DEBUG, "Getting cert chain");
   const certificate = await getCertificateChain(tenantId, decodedToken.header.kid as string);
 
+  envLogger(LogLevel.INFO, "Verifying token");
   JWT.verify(encodedToken, certificate, {
     audience: clientId.split(","),
     issuer: [`https://sts.windows.net/${tenantId}/`, `https://login.microsoftonline.com/${tenantId}/v2.0`],

tests/unit/services/azure.unitTest.ts

@@ -32,6 +32,6 @@ describe("getCertificateChain()", () => {
   it("should throw an error if no key matches the given key ID", async (): Promise<void> => {
     fetchSpy("somethingElse", "mySuperSecurePublicKey");
 
-    await expect(azure.getCertificateChain("tenantId", "keyToTheKingdom")).rejects.toThrow("no public key");
+    await expect(azure.getCertificateChain("tenantId", "otherKeyToTheKingdom")).rejects.toThrow("no public key");
   });
 });