chore: remove default value of HOSTNAME

Author: shawnhankim

README.md

@@ -90,7 +90,6 @@ js_set $awsDate                 awssig4.awsHeaderDate;
 js_set $awsPayloadHash          awssig4.awsHeaderPayloadHash;
 js_set $awsSessionToken         awscredentials.sessionToken;
 js_set $lambdaFunctionARNAuth   lambdagateway.lambdaFunctionARNAuth;
-js_var $defaultHostName         'nginx-lambda-gateway';
 
 map $request_uri $lambda_url {
     default  https://lambda.us-east-1.amazonaws.com;

core/awscredentials.js

@@ -364,15 +364,14 @@ async function _fetchEC2RoleCredentials() {
 
 /**
  * Get the credentials by assuming calling AssumeRoleWithWebIdentity with the environment variable
- * values ROLE_ARN, AWS_WEB_IDENTITY_TOKEN_FILE and HOSTNAME. The variable of
- * defaultHostName should be defined in the NGINX configuration file.
+ * values ROLE_ARN, AWS_WEB_IDENTITY_TOKEN_FILE and HOSTNAME.
  *
  * @returns {Promise<{accessKeyId: (string), secretAccessKey: (string), sessionToken: (string), expiration: (string)}>}
  * @private
  */
 async function _fetchWebIdentityCredentials(r) {
     const arn = process.env['AWS_ROLE_ARN'];
-    const name = process.env['HOSTNAME'] || r.variables.defaultHostName;
+    const name = process.env['HOSTNAME']; // The value is used for Role Session Name.
 
     let sts_endpoint = process.env['STS_ENDPOINT'];
     if (!sts_endpoint) {