feat: add support for assuming a role (#17)

* first draft attempt at adding role assumption option

* refinements

* const not var

* clean up asserts

* set explicit sts endpoint and clarify required inputs error message

* streamline mocks

* add new inputs to Action definition

* ignore .idea directory

* add initial assume role test

* make tests fail usefully when not in GitHub Actions

* add logic to handle suppression of stack trace

* pull credentials exports out into function

* convert environment variable patching to use object for source and add needed members

* add test for STS call

* compartmentalization and use custom user agent in role assumption STS client

* change DO_NOT_SUPRESS_STACK_TRACE to SHOW_STACK_TRACE

* update role-to-assume input description

Author: mattsb42-aws

Diff for: .gitignore

@@ -2,6 +2,7 @@ node_modules/
 
 # Editors
 .vscode
+.idea
 
 # Logs
 logs

Diff for: action.yml

@@ -19,6 +19,12 @@ inputs:
   mask-aws-account-id:
     description: "Whether to set the AWS account ID for these credentials as a secret value, so that it is masked in logs. Valid values are 'true' and 'false'. Defaults to true"
     required: false
+  role-to-assume:
+    description: "Use the provided credentials to assume a Role and output the assumed credentials for that Role rather than the provided credentials"
+    required: false
+  role-duration-seconds:
+    description: "Role duration in seconds (default: 6 hours)"
+    required: false
 outputs:
   aws-account-id:
     description: 'The AWS account ID for the provided credentials'

Diff for: index.js

@@ -1,5 +1,94 @@
 const core = require('@actions/core');
 const aws = require('aws-sdk');
+const assert = require('assert');
+const util = require('util');
+
+// 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.
+const MAX_ACTION_RUNTIME = 6 * 3600;
+const USER_AGENT = 'configure-aws-credentials-for-github-actions';
+
+async function assumeRole(params) {
+  // Assume a role to get short-lived credentials using longer-lived credentials.
+  const isDefined = i => !!i;
+
+  const {roleToAssume, roleDurationSeconds, accessKeyId, secretAccessKey, sessionToken, region} = params;
+  assert(
+      [roleToAssume, roleDurationSeconds, accessKeyId, secretAccessKey, region].every(isDefined),
+      "Missing required input when assuming a Role."
+  );
+
+  const {GITHUB_REPOSITORY, GITHUB_WORKFLOW, GITHUB_ACTION, GITHUB_ACTOR, GITHUB_REF, GITHUB_SHA} = process.env;
+  assert(
+      [GITHUB_REPOSITORY, GITHUB_WORKFLOW, GITHUB_ACTION, GITHUB_ACTOR, GITHUB_REF, GITHUB_SHA].every(isDefined),
+      'Missing required environment value. Are you running in GitHub Actions?'
+  );
+
+  const endpoint = util.format('https://sts.%s.amazonaws.com', region);
+
+  const sts = new aws.STS({
+    accessKeyId, secretAccessKey, sessionToken, region, endpoint, customUserAgent: USER_AGENT
+  });
+  return sts.assumeRole({
+    RoleArn: roleToAssume,
+    RoleSessionName: 'GitHubActions',
+    DurationSeconds: roleDurationSeconds,
+    Tags: [
+      {Key: 'GitHub', Value: 'Actions'},
+      {Key: 'Repository', Value: GITHUB_REPOSITORY},
+      {Key: 'Workflow', Value: GITHUB_WORKFLOW},
+      {Key: 'Action', Value: GITHUB_ACTION},
+      {Key: 'Actor', Value: GITHUB_ACTOR},
+      {Key: 'Branch', Value: GITHUB_REF},
+      {Key: 'Commit', Value: GITHUB_SHA},
+    ]
+  })
+  .promise()
+  .then(function (data) {
+    return {
+      accessKeyId: data.Credentials.AccessKeyId,
+      secretAccessKey: data.Credentials.SecretAccessKey,
+      sessionToken: data.Credentials.SessionToken,
+    };
+  });
+}
+
+function exportCredentials(params){
+  // Configure the AWS CLI and AWS SDKs using environment variables
+  const {accessKeyId, secretAccessKey, sessionToken} = params;
+
+  // AWS_ACCESS_KEY_ID:
+  // Specifies an AWS access key associated with an IAM user or role
+  core.exportVariable('AWS_ACCESS_KEY_ID', accessKeyId);
+
+  // AWS_SECRET_ACCESS_KEY:
+  // Specifies the secret key associated with the access key. This is essentially the "password" for the access key.
+  core.exportVariable('AWS_SECRET_ACCESS_KEY', secretAccessKey);
+
+  // AWS_SESSION_TOKEN:
+  // Specifies the session token value that is required if you are using temporary security credentials.
+  if (sessionToken) {
+    core.exportVariable('AWS_SESSION_TOKEN', sessionToken);
+  }
+}
+
+function exportRegion(region) {
+  // AWS_DEFAULT_REGION and AWS_REGION:
+  // Specifies the AWS Region to send requests to
+  core.exportVariable('AWS_DEFAULT_REGION', region);
+  core.exportVariable('AWS_REGION', region);
+}
+
+async function exportAccountId(maskAccountId) {
+  // Get the AWS account ID
+  const sts = new aws.STS({customUserAgent: USER_AGENT});
+  const identity = await sts.getCallerIdentity().promise();
+  const accountId = identity.Account;
+  core.setOutput('aws-account-id', accountId);
+  if (!maskAccountId || maskAccountId.toLowerCase() == 'true') {
+    core.setSecret(accountId);
+  }
+}
 
 async function run() {
   try {
@@ -9,41 +98,32 @@ async function run() {
     const region = core.getInput('aws-region', { required: true });
     const sessionToken = core.getInput('aws-session-token', { required: false });
     const maskAccountId = core.getInput('mask-aws-account-id', { required: false });
+    const roleToAssume = core.getInput('role-to-assume', {required: false});
+    const roleDurationSeconds = core.getInput('role-duration-seconds', {required: false}) || MAX_ACTION_RUNTIME;
 
-    // Configure the AWS CLI and AWS SDKs using environment variables
-
-    // AWS_ACCESS_KEY_ID:
-    // Specifies an AWS access key associated with an IAM user or role
-    core.exportVariable('AWS_ACCESS_KEY_ID', accessKeyId);
-
-    // AWS_SECRET_ACCESS_KEY:
-    // Specifies the secret key associated with the access key. This is essentially the "password" for the access key.
-    core.exportVariable('AWS_SECRET_ACCESS_KEY', secretAccessKey);
-
-    // AWS_SESSION_TOKEN:
-    // Specifies the session token value that is required if you are using temporary security credentials.
-    if (sessionToken) {
-      core.exportVariable('AWS_SESSION_TOKEN', sessionToken);
+    // Get role credentials if configured to do so
+    if (roleToAssume) {
+      const roleCredentials = await assumeRole(
+          {accessKeyId, secretAccessKey, sessionToken, region, roleToAssume, roleDurationSeconds}
+      );
+      exportCredentials(roleCredentials);
+    } else {
+      exportCredentials({accessKeyId, secretAccessKey, sessionToken});
     }
 
-    // AWS_DEFAULT_REGION and AWS_REGION:
-    // Specifies the AWS Region to send requests to
-    core.exportVariable('AWS_DEFAULT_REGION', region);
-    core.exportVariable('AWS_REGION', region);
-
-    // Get the AWS account ID
-    const sts = new aws.STS({
-      customUserAgent: 'configure-aws-credentials-for-github-actions'
-    });
-    const identity = await sts.getCallerIdentity().promise();
-    const accountId = identity.Account;
-    core.setOutput('aws-account-id', accountId);
-    if (!maskAccountId || maskAccountId.toLowerCase() == 'true') {
-      core.setSecret(accountId);
-    }
+    exportRegion(region);
+
+    await exportAccountId(maskAccountId);
   }
   catch (error) {
     core.setFailed(error.message);
+
+    const showStackTrace = process.env.SHOW_STACK_TRACE;
+
+    if (showStackTrace === 'true') {
+      throw(error)
+    }
+
   }
 }