feat(appsync): Lambda Authorizer for AppSync GraphqlApi (aws#16743)

Adds the relatively new [Lambda Authorizer for GraphqlApi](https://aws.amazon.com/blogs/mobile/appsync-lambda-auth/).

Closes: aws#16380. 

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-appsync/README.md

@@ -28,7 +28,7 @@ APIs that use GraphQL.
 
 ### DynamoDB
 
-Example of a GraphQL API with `AWS_IAM` authorization resolving into a DynamoDb
+Example of a GraphQL API with `AWS_IAM` [authorization](#authorization) resolving into a DynamoDb
 backend data source.
 
 GraphQL schema file `schema.graphql`:
@@ -345,6 +345,40 @@ If you don't specify `graphqlArn` in `fromXxxAttributes`, CDK will autogenerate
 the expected `arn` for the imported api, given the `apiId`. For creating data
 sources and resolvers, an `apiId` is sufficient.
 
+## Authorization
+
+There are multiple authorization types available for GraphQL API to cater to different
+access use cases. They are:
+
+- API Keys (`AuthorizationType.API_KEY`)
+- Amazon Cognito User Pools (`AuthorizationType.USER_POOL`)
+- OpenID Connect (`AuthorizationType.OPENID_CONNECT`)
+- AWS Identity and Access Management (`AuthorizationType.AWS_IAM`)
+- AWS Lambda (`AuthorizationType.AWS_LAMBDA`)
+
+These types can be used simultaneously in a single API, allowing different types of clients to
+access data. When you specify an authorization type, you can also specify the corresponding
+authorization mode to finish defining your authorization. For example, this is a GraphQL API
+with AWS Lambda Authorization.
+
+```ts
+authFunction = new lambda.Function(stack, 'auth-function', {});
+
+new appsync.GraphqlApi(stack, 'api', {
+  name: 'api',
+  schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+  authorizationConfig: {
+    defaultAuthorization: {
+      authorizationType: appsync.AuthorizationType.LAMBDA,
+      lambdaAuthorizerConfig: {
+        handler: authFunction, 
+        // can also specify `resultsCacheTtl` and `validationRegex`.
+      },
+    },
+  },
+});
+```
+
 ## Permissions
 
 When using `AWS_IAM` as the authorization type for GraphQL API, an IAM Role

packages/@aws-cdk/aws-appsync/lib/graphqlapi.ts

@@ -1,5 +1,6 @@
 import { IUserPool } from '@aws-cdk/aws-cognito';
 import { ManagedPolicy, Role, IRole, ServicePrincipal, Grant, IGrantable } from '@aws-cdk/aws-iam';
+import { IFunction } from '@aws-cdk/aws-lambda';
 import { CfnResource, Duration, Expiration, IResolvable, Stack } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { CfnApiKey, CfnGraphQLApi, CfnGraphQLSchema } from './appsync.generated';
@@ -29,6 +30,10 @@ export enum AuthorizationType {
    * OpenID Connect authorization type
    */
   OIDC = 'OPENID_CONNECT',
+  /**
+   * Lambda authorization type
+   */
+  LAMBDA = 'AWS_LAMBDA',
 }
 
 /**
@@ -58,6 +63,11 @@ export interface AuthorizationMode {
    * @default - none
    */
   readonly openIdConnectConfig?: OpenIdConnectConfig;
+  /**
+   * If authorizationType is `AuthorizationType.LAMBDA`, this option is required.
+   * @default - none
+   */
+  readonly lambdaAuthorizerConfig?: LambdaAuthorizerConfig;
 }
 
 /**
@@ -150,6 +160,38 @@ export interface OpenIdConnectConfig {
   readonly oidcProvider: string;
 }
 
+/**
+ * Configuration for Lambda authorization in AppSync. Note that you can only have a single AWS Lambda function configured to authorize your API.
+ */
+export interface LambdaAuthorizerConfig {
+  /**
+   * The authorizer lambda function.
+   * Note: This Lambda function must have the following resource-based policy assigned to it.
+   * When configuring Lambda authorizers in the console, this is done for you.
+   * To do so with the AWS CLI, run the following:
+   *
+   * `aws lambda add-permission --function-name "arn:aws:lambda:us-east-2:111122223333:function:my-function" --statement-id "appsync" --principal appsync.amazonaws.com --action lambda:InvokeFunction`
+   *
+   * @see https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-graphqlapi-lambdaauthorizerconfig.html
+   */
+  readonly handler: IFunction;
+
+  /**
+   * How long the results are cached.
+   * Disable caching by setting this to 0.
+   *
+   * @default Duration.minutes(5)
+   */
+  readonly resultsCacheTtl?: Duration;
+
+  /**
+   * A regular expression for validation of tokens before the Lambda function is called.
+   *
+   * @default - no regex filter will be applied.
+   */
+  readonly validationRegex?: string;
+}
+
 /**
  * Configuration of the API authorization modes.
  */
@@ -418,6 +460,7 @@ export class GraphqlApi extends GraphqlApiBase {
       logConfig: this.setupLogConfig(props.logConfig),
       openIdConnectConfig: this.setupOpenIdConnectConfig(defaultMode.openIdConnectConfig),
       userPoolConfig: this.setupUserPoolConfig(defaultMode.userPoolConfig),
+      lambdaAuthorizerConfig: this.setupLambdaAuthorizerConfig(defaultMode.lambdaAuthorizerConfig),
       additionalAuthenticationProviders: this.setupAdditionalAuthorizationModes(additionalModes),
       xrayEnabled: props.xrayEnabled,
     });
@@ -490,13 +533,19 @@ export class GraphqlApi extends GraphqlApiBase {
   }
 
   private validateAuthorizationProps(modes: AuthorizationMode[]) {
+    if (modes.filter((mode) => mode.authorizationType === AuthorizationType.LAMBDA).length > 1) {
+      throw new Error('You can only have a single AWS Lambda function configured to authorize your API.');
+    }
     modes.map((mode) => {
       if (mode.authorizationType === AuthorizationType.OIDC && !mode.openIdConnectConfig) {
         throw new Error('Missing OIDC Configuration');
       }
       if (mode.authorizationType === AuthorizationType.USER_POOL && !mode.userPoolConfig) {
         throw new Error('Missing User Pool Configuration');
       }
+      if (mode.authorizationType === AuthorizationType.LAMBDA && !mode.lambdaAuthorizerConfig) {
+        throw new Error('Missing Lambda Configuration');
+      }
     });
     if (modes.filter((mode) => mode.authorizationType === AuthorizationType.API_KEY).length > 1) {
       throw new Error('You can\'t duplicate API_KEY configuration. See https://docs.aws.amazon.com/appsync/latest/devguide/security.html');
@@ -551,13 +600,23 @@ export class GraphqlApi extends GraphqlApiBase {
     };
   }
 
+  private setupLambdaAuthorizerConfig(config?: LambdaAuthorizerConfig) {
+    if (!config) return undefined;
+    return {
+      authorizerResultTtlInSeconds: config.resultsCacheTtl?.toSeconds(),
+      authorizerUri: config.handler.functionArn,
+      identityValidationExpression: config.validationRegex,
+    };
+  }
+
   private setupAdditionalAuthorizationModes(modes?: AuthorizationMode[]) {
     if (!modes || modes.length === 0) return undefined;
     return modes.reduce<CfnGraphQLApi.AdditionalAuthenticationProviderProperty[]>((acc, mode) => [
       ...acc, {
         authenticationType: mode.authorizationType,
         userPoolConfig: this.setupUserPoolConfig(mode.userPoolConfig),
         openIdConnectConfig: this.setupOpenIdConnectConfig(mode.openIdConnectConfig),
+        lambdaAuthorizerConfig: this.setupLambdaAuthorizerConfig(mode.lambdaAuthorizerConfig),
       },
     ], []);
   }

packages/@aws-cdk/aws-appsync/test/appsync-auth.test.ts

@@ -1,6 +1,7 @@
 import * as path from 'path';
 import { Template } from '@aws-cdk/assertions';
 import * as cognito from '@aws-cdk/aws-cognito';
+import * as lambda from '@aws-cdk/aws-lambda';
 import * as cdk from '@aws-cdk/core';
 import * as appsync from '../lib';
 
@@ -630,3 +631,206 @@ describe('AppSync OIDC Authorization', () => {
     });
   });
 });
+
+describe('AppSync Lambda Authorization', () => {
+  let fn: lambda.Function;
+  beforeEach(() => {
+    fn = new lambda.Function(stack, 'auth-function', {
+      runtime: lambda.Runtime.NODEJS_12_X,
+      handler: 'index.handler',
+      code: lambda.Code.fromInline('/* lambda authentication code here.*/'),
+    });
+  });
+
+  test('Lambda authorization configurable in default authorization has default configuration', () => {
+    // WHEN
+    new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        defaultAuthorization: {
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          lambdaAuthorizerConfig: {
+            handler: fn,
+          },
+        },
+      },
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::AppSync::GraphQLApi', {
+      AuthenticationType: 'AWS_LAMBDA',
+      LambdaAuthorizerConfig: {
+        AuthorizerUri: {
+          'Fn::GetAtt': [
+            'authfunction96361832',
+            'Arn',
+          ],
+        },
+      },
+    });
+  });
+
+  test('Lambda authorization configurable in default authorization', () => {
+    // WHEN
+    new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        defaultAuthorization: {
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          lambdaAuthorizerConfig: {
+            handler: fn,
+            resultsCacheTtl: cdk.Duration.seconds(300),
+            validationRegex: 'custom-.*',
+          },
+        },
+      },
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::AppSync::GraphQLApi', {
+      AuthenticationType: 'AWS_LAMBDA',
+      LambdaAuthorizerConfig: {
+        AuthorizerUri: {
+          'Fn::GetAtt': [
+            'authfunction96361832',
+            'Arn',
+          ],
+        },
+        AuthorizerResultTtlInSeconds: 300,
+        IdentityValidationExpression: 'custom-.*',
+      },
+    });
+  });
+
+  test('Lambda authorization configurable in additional authorization has default configuration', () => {
+    // WHEN
+    new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        additionalAuthorizationModes: [{
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          lambdaAuthorizerConfig: {
+            handler: fn,
+          },
+        }],
+      },
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::AppSync::GraphQLApi', {
+      AdditionalAuthenticationProviders: [{
+        AuthenticationType: 'AWS_LAMBDA',
+        LambdaAuthorizerConfig: {
+          AuthorizerUri: {
+            'Fn::GetAtt': [
+              'authfunction96361832',
+              'Arn',
+            ],
+          },
+        },
+      }],
+    });
+  });
+
+  test('Lambda authorization configurable in additional authorization', () => {
+    // WHEN
+    new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        additionalAuthorizationModes: [{
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          lambdaAuthorizerConfig: {
+            handler: fn,
+            resultsCacheTtl: cdk.Duration.seconds(300),
+            validationRegex: 'custom-.*',
+          },
+        }],
+      },
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::AppSync::GraphQLApi', {
+      AdditionalAuthenticationProviders: [{
+        AuthenticationType: 'AWS_LAMBDA',
+        LambdaAuthorizerConfig: {
+          AuthorizerUri: {
+            'Fn::GetAtt': [
+              'authfunction96361832',
+              'Arn',
+            ],
+          },
+          AuthorizerResultTtlInSeconds: 300,
+          IdentityValidationExpression: 'custom-.*',
+        },
+      }],
+    });
+  });
+
+  test('Lambda authorization throws with multiple lambda authorization', () => {
+    expect(() => new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        defaultAuthorization: {
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          lambdaAuthorizerConfig: {
+            handler: fn,
+          },
+        },
+        additionalAuthorizationModes: [
+          {
+            authorizationType: appsync.AuthorizationType.LAMBDA,
+            lambdaAuthorizerConfig: {
+              handler: fn,
+              resultsCacheTtl: cdk.Duration.seconds(300),
+              validationRegex: 'custom-.*',
+            },
+          },
+        ],
+      },
+    })).toThrow('You can only have a single AWS Lambda function configured to authorize your API.');
+
+    expect(() => new appsync.GraphqlApi(stack, 'api2', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        defaultAuthorization: { authorizationType: appsync.AuthorizationType.IAM },
+        additionalAuthorizationModes: [
+          {
+            authorizationType: appsync.AuthorizationType.LAMBDA,
+            lambdaAuthorizerConfig: {
+              handler: fn,
+              resultsCacheTtl: cdk.Duration.seconds(300),
+              validationRegex: 'custom-.*',
+            },
+          },
+          {
+            authorizationType: appsync.AuthorizationType.LAMBDA,
+            lambdaAuthorizerConfig: {
+              handler: fn,
+              resultsCacheTtl: cdk.Duration.seconds(300),
+              validationRegex: 'custom-.*',
+            },
+          },
+        ],
+      },
+    })).toThrow('You can only have a single AWS Lambda function configured to authorize your API.');
+  });
+
+  test('throws if authorization type and mode do not match', () => {
+    expect(() => new appsync.GraphqlApi(stack, 'api', {
+      name: 'api',
+      schema: appsync.Schema.fromAsset(path.join(__dirname, 'appsync.test.graphql')),
+      authorizationConfig: {
+        defaultAuthorization: {
+          authorizationType: appsync.AuthorizationType.LAMBDA,
+          openIdConnectConfig: { oidcProvider: 'test' },
+        },
+      },
+    })).toThrow('Missing Lambda Configuration');
+  });
+});