feat: add regex validation to role-session-name (#1765)

Previously invalid role session names would get errors from the STS
API instead of this action rejecting them, causing unnecessary retries.
Now we check them and fail early.

Closes #1656. That FR recommended that we sanitize the name before
sending to STS, but instead we error to not silently change the user's
selected session name (avoiding the potential security sharp edge)

src/index.ts

@@ -19,6 +19,7 @@ import { writeProfileFiles } from './profileManager';
 const DEFAULT_ROLE_DURATION = 3600; // One hour (seconds)
 const ROLE_SESSION_NAME = 'GitHubActions';
 const REGION_REGEX = /^[a-z0-9-]+$/g;
+const ROLE_SESSION_NAME_REGEX = /^[\w+=,.@-]*$/;
 
 export async function run() {
   try {
@@ -129,6 +130,17 @@ export async function run() {
       throw new Error(`Region is not valid: ${region}`);
     }
 
+    if (roleSessionName.length < 2 || roleSessionName.length > 64) {
+      throw new Error(
+        `Role session name must be between 2 and 64 characters, got ${roleSessionName.length}: '${roleSessionName}'`,
+      );
+    }
+    if (!roleSessionName.match(ROLE_SESSION_NAME_REGEX)) {
+      throw new Error(
+        `Role session name is not valid: '${roleSessionName}'. Must satisfy regular expression pattern: [\\w+=,.@-]*`,
+      );
+    }
+
     exportRegion(region, outputEnvCredentials);
 
     // Instantiate credentials client