feat: Add the ability to use a web identity token file (#240)

* feat: Add the ability to use a web identity token file

* mark web identity token file as not required

* fix indentation

* better docs and added support for relative vs absolute paths

* bind sts context and adjust fs calls

* exclude tags if using web identity token file

* fix readme aand adjust tag removal logic

* undo re-ordering of lines

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: nesta219

README.md

@@ -189,6 +189,17 @@ with:
 ```
 In this case, your runner's credentials must have permissions to assume the role.
 
+You can also assume a role using a web identity token file, such as if using [Amazon EKS IRSA](https://docs.aws.amazon.com/eks/latest/userguide/iam-roles-for-service-accounts-technical-overview.html).  Pods running in EKS worker nodes that do not run as root can use this file to assume a role with a web identity.
+
+You can configure your workflow as follows in order to use this file:
+```yaml
+uses: aws-actions/configure-aws-credentials@v1
+with:
+  aws-region: us-east-2
+  role-to-assume: my-github-actions-role
+  web-identity-token-file: /var/run/secrets/eks.amazonaws.com/serviceaccount/token
+```
+
 ### Use with the AWS CLI
 
 This workflow does _not_ install the [AWS CLI](https://aws.amazon.com/cli/) into your environment. Self-hosted runners that intend to run this action prior to executing `aws` commands need to have the AWS CLI [installed](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-install.html) if it's not already present. 

action.yml

@@ -34,6 +34,11 @@ inputs:
       environment with the assumed role credentials rather than with the provided
       credentials
     required: false
+  web-identity-token-file:
+    description: >-
+      Use the web identity token file from the provided file system path in order to
+      assume an IAM role using a web identity. E.g., from within an Amazon EKS worker node
+    required: false
   role-duration-seconds:
     description: "Role duration in seconds (default: 6 hours)"
     required: false

index.js

@@ -1,6 +1,8 @@
 const core = require('@actions/core');
 const aws = require('aws-sdk');
 const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
 
 // The max time that a GitHub action is allowed to run is 6 hours.
 // That seems like a reasonable default to use if no role duration is defined.
@@ -22,7 +24,8 @@ async function assumeRole(params) {
     roleDurationSeconds,
     roleSessionName,
     region,
-    roleSkipSessionTagging
+    roleSkipSessionTagging,
+    webIdentityTokenFile
   } = params;
   assert(
       [sourceAccountId, roleToAssume, roleDurationSeconds, roleSessionName, region].every(isDefined),
@@ -42,6 +45,7 @@ async function assumeRole(params) {
     // Supports only 'aws' partition. Customers in other partitions ('aws-cn') will need to provide full ARN
     roleArn = `arn:aws:iam::${sourceAccountId}:role/${roleArn}`;
   }
+
   const tagArray = [
     {Key: 'GitHub', Value: 'Actions'},
     {Key: 'Repository', Value: GITHUB_REPOSITORY},
@@ -74,15 +78,38 @@ async function assumeRole(params) {
     assumeRoleRequest.ExternalId = roleExternalId;
   }
 
-  return sts.assumeRole(assumeRoleRequest)
-  .promise()
-  .then(function (data) {
-    return {
-      accessKeyId: data.Credentials.AccessKeyId,
-      secretAccessKey: data.Credentials.SecretAccessKey,
-      sessionToken: data.Credentials.SessionToken,
-    };
-  });
+  let assumeFunction = sts.assumeRole.bind(sts);
+
+  if(isDefined(webIdentityTokenFile)) {
+    core.debug("webIdentityTokenFile provided. Will call sts:AssumeRoleWithWebIdentity and take session tags from token contents.")
+    delete assumeRoleRequest.Tags;
+
+    const webIdentityTokenFilePath = path.isAbsolute(webIdentityTokenFile) ?
+      webIdentityTokenFile :
+      path.join(process.env.GITHUB_WORKSPACE, webIdentityTokenFile);
+
+    if (!fs.existsSync(webIdentityTokenFilePath)) {
+      throw new Error(`Web identity token file does not exist: ${webIdentityTokenFilePath}`);
+    }
+
+    try {
+      assumeRoleRequest.WebIdentityToken = await fs.promises.readFile(webIdentityTokenFilePath, 'utf8');
+      assumeFunction = sts.assumeRoleWithWebIdentity.bind(sts);
+    } catch(error) {
+      throw new Error(`Web identity token file could not be read: ${error.message}`);
+    }
+    
+  } 
+
+  return assumeFunction(assumeRoleRequest)
+    .promise()
+    .then(function (data) {
+      return {
+        accessKeyId: data.Credentials.AccessKeyId,
+        secretAccessKey: data.Credentials.SecretAccessKey,
+        sessionToken: data.Credentials.SessionToken,
+      };
+    });
 }
 
 function sanitizeGithubActor(actor) {
@@ -211,6 +238,7 @@ async function run() {
     const roleSessionName = core.getInput('role-session-name', { required: false }) || ROLE_SESSION_NAME;
     const roleSkipSessionTaggingInput = core.getInput('role-skip-session-tagging', { required: false })|| 'false';
     const roleSkipSessionTagging = roleSkipSessionTaggingInput.toLowerCase() === 'true';
+    const webIdentityTokenFile = core.getInput('web-identity-token-file', { required: false })
 
     if (!region.match(REGION_REGEX)) {
       throw new Error(`Region is not valid: ${region}`);
@@ -249,7 +277,8 @@ async function run() {
         roleExternalId,
         roleDurationSeconds,
         roleSessionName,
-        roleSkipSessionTagging
+        roleSkipSessionTagging,
+        webIdentityTokenFile
       });
       exportCredentials(roleCredentials);
       await validateCredentials(roleCredentials.accessKeyId);

index.test.js

@@ -24,6 +24,7 @@ const ENVIRONMENT_VARIABLE_OVERRIDES = {
     GITHUB_ACTOR: 'MY-USERNAME[bot]',
     GITHUB_SHA: 'MY-COMMIT-ID',
     GITHUB_REF: 'MY-BRANCH',
+    GITHUB_WORKSPACE: '/home/github'
 };
 const GITHUB_ACTOR_SANITIZED = 'MY-USERNAME_bot_'
 
@@ -46,6 +47,7 @@ const ASSUME_ROLE_INPUTS = {...CREDS_INPUTS, 'role-to-assume': ROLE_ARN, 'aws-re
 
 const mockStsCallerIdentity = jest.fn();
 const mockStsAssumeRole = jest.fn();
+const mockStsAssumeRoleWithWebIdentity = jest.fn();
 
 jest.mock('aws-sdk', () => {
     return {
@@ -55,10 +57,20 @@ jest.mock('aws-sdk', () => {
         STS: jest.fn(() => ({
             getCallerIdentity: mockStsCallerIdentity,
             assumeRole: mockStsAssumeRole,
+            assumeRoleWithWebIdentity: mockStsAssumeRoleWithWebIdentity
         }))
     };
 });
 
+jest.mock('fs', () => {
+    return {
+        promises: {
+            readFile: jest.fn(() => Promise.resolve('testpayload')),
+        },
+        existsSync: jest.fn(() => true)
+    };
+});
+
 describe('Configure AWS Credentials', () => {
     const OLD_ENV = process.env;
 
@@ -119,6 +131,20 @@ describe('Configure AWS Credentials', () => {
                 }
             }
         });
+
+        mockStsAssumeRoleWithWebIdentity.mockImplementation(() => {
+            return {
+                promise() {
+                    return Promise.resolve({
+                        Credentials: {
+                            AccessKeyId: FAKE_STS_ACCESS_KEY_ID,
+                            SecretAccessKey: FAKE_STS_SECRET_ACCESS_KEY,
+                            SessionToken: FAKE_STS_SESSION_TOKEN
+                        }
+                    });
+                }
+            }
+        });
     });
 
     afterEach(() => {
@@ -507,6 +533,34 @@ describe('Configure AWS Credentials', () => {
         })
     });
 
+    test('web identity token file provided with absolute path', async () => {
+        core.getInput = jest
+            .fn()
+            .mockImplementation(mockGetInput({'role-to-assume': ROLE_ARN, 'aws-region': FAKE_REGION, 'web-identity-token-file': '/fake/token/file'}));
+
+        await run();
+        expect(mockStsAssumeRoleWithWebIdentity).toHaveBeenCalledWith({
+            RoleArn: 'arn:aws:iam::111111111111:role/MY-ROLE',
+            RoleSessionName: 'GitHubActions',
+            DurationSeconds: 6 * 3600,
+            WebIdentityToken: 'testpayload'
+        })
+    });
+
+    test('web identity token file provided with relative path', async () => {
+        core.getInput = jest
+            .fn()
+            .mockImplementation(mockGetInput({'role-to-assume': ROLE_ARN, 'aws-region': FAKE_REGION, 'web-identity-token-file': 'fake/token/file'}));
+
+        await run();
+        expect(mockStsAssumeRoleWithWebIdentity).toHaveBeenCalledWith({
+            RoleArn: 'arn:aws:iam::111111111111:role/MY-ROLE',
+            RoleSessionName: 'GitHubActions',
+            DurationSeconds: 6 * 3600,
+            WebIdentityToken: 'testpayload'
+        })
+    });
+
     test('role external ID provided', async () => {
         core.getInput = jest
             .fn()