feat: allow aws credentials to be provided in other ways

README.md

@@ -8,6 +8,8 @@ This is a wallet or signer that can be used together with [Ethers.js](https://gi
 npm i ethers-aws-kms-signer
 ```
 
+You can provide the AWS Credentials using the various ways listed [here](https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/setting-credentials-node.html) depending on how you are using this library. You can also explicitly specify them when invoking the `AwsKmsSigner` constructor as shown below.
+
 ```js
 import { AwsKmsSigner } from "ethers-aws-kms-signer";
 

src/index.ts

@@ -2,8 +2,9 @@ import { ethers } from "ethers";
 import { getPublicKey, getEthereumAddress, requestKmsSignature, determineCorrectV } from "./util/aws-kms-utils";
 
 export interface AwsKmsSignerCredentials {
-  accessKeyId: string;
-  secretAccessKey: string;
+  accessKeyId?: string;
+  secretAccessKey?: string;
+  sessionToken?: string;
   region: string;
   keyId: string;
 }