feat: idempotent fetch (#1289)

* Add functionality to re-use existing credentials

* Finish adding use-existing-credentials logic

* Add testing for use-existing-credentials

* Update README

* feat: finalize use-exisiting-credentials feature

---------

Co-authored-by: Tom Keller <kellertk@amazon.com>

src/helpers.ts

@@ -144,3 +144,16 @@ export function isDefined<T>(i: T | undefined | null): i is T {
   return i !== undefined && i !== null;
 }
 /* c8 ignore stop */
+
+export async function areCredentialsValid(credentialsClient: CredentialsClient) {
+  const client = credentialsClient.stsClient;
+  try {
+    const identity = await client.send(new GetCallerIdentityCommand({}));
+    if (identity.Account) {
+      return true;
+    }
+    return false;
+  } catch (_) {
+    return false;
+  }
+}

src/index.ts

@@ -3,6 +3,7 @@ import type { AssumeRoleCommandOutput } from '@aws-sdk/client-sts';
 import { CredentialsClient } from './CredentialsClient';
 import { assumeRole } from './assumeRole';
 import {
+  areCredentialsValid,
   errorMessage,
   exportAccountId,
   exportCredentials,
@@ -60,6 +61,8 @@ export async function run() {
     const specialCharacterWorkaroundInput =
       core.getInput('special-characters-workaround', { required: false }) || 'false';
     const specialCharacterWorkaround = specialCharacterWorkaroundInput.toLowerCase() === 'true';
+    const useExistingCredentialsInput = core.getInput('use-existing-credentials', { required: false }) || 'false';
+    const useExistingCredentials = useExistingCredentialsInput.toLowerCase() === 'true';
     let maxRetries = Number.parseInt(core.getInput('retry-max-attempts', { required: false })) || 12;
     switch (true) {
       case specialCharacterWorkaround:
@@ -116,6 +119,16 @@ export async function run() {
     let sourceAccountId: string;
     let webIdentityToken: string;
 
+    //if the user wants to attempt to use existing credentials, check if we have some already
+    if (useExistingCredentials) {
+      const validCredentials = await areCredentialsValid(credentialsClient);
+      if (validCredentials) {
+        core.notice('Pre-existing credentials are valid. No need to generate new ones.');
+        return;
+      }
+      core.notice('No valid credentials exist. Running as normal.');
+    }
+
     // If OIDC is being used, generate token
     // Else, export credentials provided as input
     if (useGitHubOIDCProvider()) {