feat(aws-dynamodb): IAM grants support (#870)

Adds the following grant APIs to dynamodb.Table:

- grant(principal, ...actions)
- grantReadData(principal)
- grantWriteData(principal)
- grantReadWriteData(principal)
- grantFullAccess(principal)

Author: Elad Ben-Israel

Diff for: packages/@aws-cdk/aws-dynamodb/lib/table.ts

@@ -1,11 +1,27 @@
 import { cloudformation as applicationautoscaling } from '@aws-cdk/aws-applicationautoscaling';
-import { PolicyStatement, PolicyStatementEffect, Role, ServicePrincipal } from '@aws-cdk/aws-iam';
+import iam = require('@aws-cdk/aws-iam');
 import { Construct, TagManager, Tags } from '@aws-cdk/cdk';
 import { cloudformation as dynamodb } from './dynamodb.generated';
 
 const HASH_KEY_TYPE = 'HASH';
 const RANGE_KEY_TYPE = 'RANGE';
 
+const READ_DATA_ACTIONS = [
+  'dynamodb:BatchGetItem',
+  'dynamodb:GetRecords',
+  'dynamodb:GetShardIterator',
+  'dynamodb:Query',
+  'dynamodb:GetItem',
+  'dynamodb:Scan'
+];
+
+const WRITE_DATA_ACTIONS = [
+  'dynamodb:BatchWriteItem',
+  'dynamodb:PutItem',
+  'dynamodb:UpdateItem',
+  'dynamodb:DeleteItem'
+];
+
 export interface Attribute {
   /**
    * The name of an attribute.
@@ -314,6 +330,57 @@ export class Table extends Construct {
     this.writeScalingPolicyResource = this.buildAutoScaling(this.writeScalingPolicyResource, 'Write', props);
   }
 
+  /**
+   * Adds an IAM policy statement associated with this table to an IAM
+   * principal's policy.
+   * @param principal The principal (no-op if undefined)
+   * @param actions The set of actions to allow (i.e. "dynamodb:PutItem", "dynamodb:GetItem", ...)
+   */
+  public grant(principal?: iam.IPrincipal, ...actions: string[]) {
+    if (!principal) {
+      return;
+    }
+    principal.addToPolicy(new iam.PolicyStatement()
+      .addResource(this.tableArn)
+      .addActions(...actions));
+  }
+
+  /**
+   * Permits an IAM principal all data read operations from this table:
+   * BatchGetItem, GetRecords, GetShardIterator, Query, GetItem, Scan.
+   * @param principal The principal to grant access to
+   */
+  public grantReadData(principal?: iam.IPrincipal) {
+    this.grant(principal, ...READ_DATA_ACTIONS);
+  }
+
+  /**
+   * Permits an IAM principal all data write operations to this table:
+   * BatchWriteItem, PutItem, UpdateItem, DeleteItem.
+   * @param principal The principal to grant access to
+   */
+  public grantWriteData(principal?: iam.IPrincipal) {
+    this.grant(principal, ...WRITE_DATA_ACTIONS);
+  }
+
+  /**
+   * Permits an IAM principal to all data read/write operations to this table.
+   * BatchGetItem, GetRecords, GetShardIterator, Query, GetItem, Scan,
+   * BatchWriteItem, PutItem, UpdateItem, DeleteItem
+   * @param principal The principal to grant access to
+   */
+  public grantReadWriteData(principal?: iam.IPrincipal) {
+    this.grant(principal, ...READ_DATA_ACTIONS, ...WRITE_DATA_ACTIONS);
+  }
+
+  /**
+   * Permits all DynamoDB operations ("dynamodb:*") to an IAM principal.
+   * @param principal The principal to grant access to
+   */
+  public grantFullAccess(principal?: iam.IPrincipal) {
+    this.grant(principal, 'dynamodb:*');
+  }
+
   /**
    * Validate the table construct.
    *
@@ -443,21 +510,21 @@ export class Table extends Construct {
   }
 
   private buildAutoScalingRole(roleResourceName: string) {
-    const autoScalingRole = new Role(this, roleResourceName, {
-      assumedBy: new ServicePrincipal('application-autoscaling.amazonaws.com')
+    const autoScalingRole = new iam.Role(this, roleResourceName, {
+      assumedBy: new iam.ServicePrincipal('application-autoscaling.amazonaws.com')
     });
-    autoScalingRole.addToPolicy(new PolicyStatement(PolicyStatementEffect.Allow)
+    autoScalingRole.addToPolicy(new iam.PolicyStatement(iam.PolicyStatementEffect.Allow)
       .addActions("dynamodb:DescribeTable", "dynamodb:UpdateTable")
       .addResource(this.tableArn));
-    autoScalingRole.addToPolicy(new PolicyStatement(PolicyStatementEffect.Allow)
+    autoScalingRole.addToPolicy(new iam.PolicyStatement(iam.PolicyStatementEffect.Allow)
       .addActions("cloudwatch:PutMetricAlarm", "cloudwatch:DescribeAlarms", "cloudwatch:GetMetricStatistics",
         "cloudwatch:SetAlarmState", "cloudwatch:DeleteAlarms")
       .addAllResources());
     return autoScalingRole;
   }
 
   private buildScalableTargetResourceProps(scalableDimension: string,
-                                           scalingRole: Role,
+                                           scalingRole: iam.Role,
                                            props: AutoScalingProps) {
     return {
       maxCapacity: props.maxCapacity,

Diff for: packages/@aws-cdk/aws-dynamodb/test/test.dynamodb.ts

@@ -1,3 +1,5 @@
+import { expect, haveResource } from '@aws-cdk/assert';
+import iam = require('@aws-cdk/aws-iam');
 import { App, Stack } from '@aws-cdk/cdk';
 import { Test } from 'nodeunit';
 import {
@@ -10,6 +12,8 @@ import {
   Table
 } from '../lib';
 
+// tslint:disable:object-literal-key-quotes
+
 // CDK parameters
 const STACK_NAME = 'MyStack';
 const CONSTRUCT_NAME = 'MyTable';
@@ -2024,6 +2028,34 @@ export = {
     }), /minimumCapacity must be greater than or equal to 0; Provided value is: -5/);
 
     test.done();
+  },
+
+  'grants': {
+
+    '"grant" allows adding arbitrary actions associated with this table resource'(test: Test) {
+      testGrant(test,
+        [ 'action1', 'action2' ], (p, t) => t.grant(p, 'dynamodb:action1', 'dynamodb:action2'));
+    },
+
+    '"grantReadData" allows the principal to read data from the table'(test: Test) {
+      testGrant(test,
+        [ 'BatchGetItem', 'GetRecords', 'GetShardIterator', 'Query', 'GetItem', 'Scan' ], (p, t) => t.grantReadData(p));
+    },
+
+    '"grantWriteData" allows the principal to write data to the table'(test: Test) {
+      testGrant(test, [
+        'BatchWriteItem', 'PutItem', 'UpdateItem', 'DeleteItem' ], (p, t) => t.grantWriteData(p));
+    },
+
+    '"grantReadWriteData" allows the principal to read/write data'(test: Test) {
+      testGrant(test, [
+        'BatchGetItem', 'GetRecords', 'GetShardIterator', 'Query', 'GetItem', 'Scan',
+        'BatchWriteItem', 'PutItem', 'UpdateItem', 'DeleteItem' ], (p, t) => t.grantReadWriteData(p));
+    },
+
+    '"grantFullAccess" allows the principal to perform any action on the table ("*")'(test: Test) {
+      testGrant(test, [ '*' ], (p, t) => t.grantFullAccess(p));
+    }
   }
 };
 
@@ -2036,3 +2068,38 @@ class TestApp {
     return this.app.synthesizeStack(this.stack.name).template;
   }
 }
+
+function testGrant(test: Test, expectedActions: string[], invocation: (user: iam.IPrincipal, table: Table) => void) {
+  // GIVEN
+  const stack = new Stack();
+
+  const table = new Table(stack, 'my-table');
+  table.addPartitionKey({ name: 'ID', type:  AttributeType.String });
+
+  const user = new iam.User(stack, 'user');
+
+  // WHEN
+  invocation(user, table);
+
+  // THEN
+  const action = expectedActions.length > 1 ? expectedActions.map(a => `dynamodb:${a}`) : `dynamodb:${expectedActions[0]}`;
+  expect(stack).to(haveResource('AWS::IAM::Policy', {
+    "PolicyDocument": {
+      "Statement": [
+        {
+          "Action": action,
+          "Effect": "Allow",
+          "Resource": {
+            "Fn::GetAtt": [
+              "mytable0324D45C",
+              "Arn"
+            ]
+          }
+        }
+      ],
+      "Version": "2012-10-17"
+    },
+    "Users": [ { "Ref": "user2C2B57AE" } ]
+  }));
+  test.done();
+}