feat(http-exception-filter): add option to mask headers

packages/http-exception-filter/src/http-exception-filter.ts

@@ -1,16 +1,70 @@
 import { ArgumentsHost, Catch, ExceptionFilter, HttpException, HttpStatus, Logger } from '@nestjs/common';
 import { HttpArgumentsHost } from '@nestjs/common/interfaces';
-import { Response } from 'express';
+import { Request, Response } from 'express';
 import { get } from 'lodash';
 import { getCode, getErrorMessage } from './error.utils';
 
+/**
+ * Option to mask headers
+ */
+export type MaskHeaders = Record<string, boolean | ((headerValue: string | string[]) => unknown)>;
+
+/**
+ * HttpExceptionFilter options
+ */
+export interface HttpExceptionFilterOptions {
+  /**
+   * Disable the masking of headers
+   * @default false
+   */
+  disableMasking?: boolean;
+
+  /**
+   * Placeholder to use when masking a header
+   * @default '****';
+   */
+  maskingPlaceholder?: string;
+
+  /**
+   * Mask configuration
+   */
+  mask?: {
+    /**
+     * The headers to mask with their mask configuration
+     * - `true` to replace the header value with the `maskingPlaceholder`
+     * - a function to replace the header value with the result of the function
+     * @example
+     * ```ts
+     * mask: {
+     *  requestHeader: {
+     *    // log authorization type only
+     *   'authorization': (headerValue: string) => headerValue.split(' ')[0],
+     *   'x-api-key': true,
+     *  }
+     * }
+     * ```
+     */
+    requestHeader?: MaskHeaders;
+  };
+}
+
 /**
  * Catch and format thrown exception in NestJS application based on Express
  */
 @Catch()
 export class HttpExceptionFilter implements ExceptionFilter {
   private readonly logger: Logger = new Logger(HttpExceptionFilter.name);
 
+  private readonly disableMasking: boolean;
+  private readonly maskingPlaceholder: string;
+  private readonly mask: HttpExceptionFilterOptions['mask'];
+
+  constructor(options?: HttpExceptionFilterOptions) {
+    this.disableMasking = options?.disableMasking ?? false;
+    this.maskingPlaceholder = options?.maskingPlaceholder ?? '****';
+    this.mask = options?.mask ?? {};
+  }
+
   /**
    * Catch and format thrown exception
    */
@@ -50,15 +104,15 @@ export class HttpExceptionFilter implements ExceptionFilter {
       this.logger.error(
         {
           message: `${status} [${request.method} ${request.url}] has thrown a critical error`,
-          headers: request.headers,
+          headers: this.maskHeaders(request.headers),
         },
         exceptionStack,
       );
     } else if (status >= HttpStatus.BAD_REQUEST) {
       this.logger.warn({
         message: `${status} [${request.method} ${request.url}] has thrown an HTTP client error`,
         exceptionStack,
-        headers: request.headers,
+        headers: this.maskHeaders(request.headers),
       });
     }
     response.status(status).send({
@@ -67,4 +121,52 @@ export class HttpExceptionFilter implements ExceptionFilter {
       status,
     });
   }
+
+  /**
+   * Mask the given headers
+   * @param headers the headers to mask
+   * @returns the masked headers
+   */
+  private maskHeaders(headers: Request['headers']): Record<string, unknown> {
+    if (this.disableMasking || this.mask?.requestHeader === undefined) {
+      return headers;
+    }
+
+    return Object.keys(headers).reduce<Record<string, unknown>>(
+      (maskedHeaders: Record<string, unknown>, headerKey: string): Record<string, unknown> => {
+        const headerValue = headers[headerKey];
+        const mask = this.mask?.requestHeader?.[headerKey];
+
+        if (headerValue === undefined) {
+          return maskedHeaders;
+        }
+
+        if (mask === true) {
+          return {
+            ...maskedHeaders,
+            [headerKey]: this.maskingPlaceholder,
+          };
+        }
+
+        if (typeof mask === 'function') {
+          try {
+            return {
+              ...maskedHeaders,
+              [headerKey]: mask(headerValue),
+            };
+          } catch (error) {
+            this.logger.warn(`HttpFilterOptions - Masking error for header ${headerKey}`, { error, mask, headerKey });
+
+            return {
+              ...maskedHeaders,
+              [headerKey]: this.maskingPlaceholder,
+            };
+          }
+        }
+
+        return maskedHeaders;
+      },
+      headers,
+    );
+  }
 }

packages/http-exception-filter/test/http-exception-filter.test.ts

@@ -15,7 +15,17 @@ describe('Http Exception Filter', () => {
     app = moduleRef.createNestApplication();
     app.useLogger(Logger);
     app.useGlobalPipes(new ValidationPipe());
-    app.useGlobalFilters(new HttpExceptionFilter());
+    app.useGlobalFilters(
+      new HttpExceptionFilter({
+        mask: {
+          requestHeader: {
+            authorization: (headerValue: string | string[]) =>
+              typeof headerValue === 'string' ? headerValue.split(' ')[0] : undefined,
+            'x-api-key': true,
+          },
+        },
+      }),
+    );
 
     await app.init();
   });
@@ -156,4 +166,30 @@ describe('Http Exception Filter', () => {
       status: 413,
     });
   });
+
+  it('should mask the headers', async () => {
+    const warnSpy: jest.SpyInstance = jest.spyOn(Logger.prototype, 'warn');
+    const url: string = `/cats/notfound`;
+
+    const { body: resBody } = await request(app.getHttpServer())
+      .get(url)
+      .set('Authorization', 'Bearer 123456')
+      .set('X-API-Key', '123456')
+      .expect(HttpStatus.NOT_FOUND);
+
+    expect(resBody).toEqual({
+      code: 'UNKNOWN_ENTITY',
+      message: 'Id notfound could not be found',
+      status: 404,
+    });
+
+    expect(warnSpy).toHaveBeenCalledWith({
+      message: `404 [GET ${url}] has thrown an HTTP client error`,
+      exceptionStack: expect.any(String),
+      headers: expect.objectContaining({
+        authorization: 'Bearer',
+        'x-api-key': '****',
+      }),
+    });
+  });
 });