feat: expose run id in STS client user-agent (#1774)

* feat: expose run id in STS client user-agent

Closes #483.
This commit modifies the user-agent string so that it includes the
GITHUB_RUN_ID and the GITHUB_RUN_ATTEMPT, in the format typically used
by the SDK. User agent strings are logged to CloudTrail, allowing users
to correlate CloudTrail events with GHA runs. We took this approach
instead of logging the ACCESS_KEY_ID as suggested in the issue to avoid
logging sensitive information.

* feat: add github_action to ua string

src/helpers.ts

@@ -1,11 +1,32 @@
 import * as core from '@actions/core';
 import type { Credentials, STSClient } from '@aws-sdk/client-sts';
 import { GetCallerIdentityCommand } from '@aws-sdk/client-sts';
+import type { UserAgent } from '@smithy/types';
 import type { CredentialsClient } from './CredentialsClient';
 
 const MAX_TAG_VALUE_LENGTH = 256;
 const SANITIZATION_CHARACTER = '_';
 const SPECIAL_CHARS_REGEX = /[!@#$%^&*()_+\-=[\]{};':"\\|,.<>/?]+/;
+const USER_AGENT_PREFIX = 'configure-aws-credentials-for-github-actions';
+const UA_FIELDS: ReadonlyArray<{ env: string; label: string; pattern: RegExp }> = [
+  { env: 'GITHUB_ACTION', label: 'action', pattern: /^[A-Za-z0-9_-]{1,128}$/ },
+  { env: 'GITHUB_RUN_ID', label: 'run_id', pattern: /^[0-9]{1,20}$/ },
+  { env: 'GITHUB_RUN_ATTEMPT', label: 'attempt', pattern: /^[0-9]{1,10}$/ },
+];
+
+export function buildCustomUserAgent(): UserAgent {
+  const tokens: UserAgent = [[USER_AGENT_PREFIX]];
+  for (const { env, label, pattern } of UA_FIELDS) {
+    const value = process.env[env];
+    if (value === undefined) continue;
+    if (pattern.test(value)) {
+      tokens.push(['md', `${label}#${value}`]);
+    } else {
+      core.warning(`${env} has unexpected format; omitting from User-Agent`);
+    }
+  }
+  return tokens;
+}
 
 export function translateEnvVariables() {
   const envVars = [