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Fetches STS credentials to be used when connecting to other AWS services.


To install this middleware you can use NPM:

npm install --save @middy/sts
npm install --save-dev @aws-sdk/client-sts


  • AwsClient (object) (default STSClient): STSClient class constructor (i.e. that has been instrumented with AWS XRay). Must be from @aws-sdk/client-sts.
  • awsClientOptions (object) (optional): Options to pass to STSClient class constructor.
  • awsClientCapture (function) (optional): Enable XRay by passing captureAWSv3Client from aws-xray-sdk in.
  • fetchData (object) (required): Mapping of internal key name to API request parameters.
  • disablePrefetch (boolean) (default false): On cold start requests will trigger early if they can. Setting awsClientAssumeRole disables prefetch.
  • cacheKey (string) (default sts): Cache key for the fetched data responses. Must be unique across all middleware.
  • cacheExpiry (number) (default -1): How long fetch data responses should be cached for. -1: cache forever, 0: never cache, n: cache for n ms.
  • setToContext (boolean) (default false): Store credentials to request.context.


  • Lambda is required to have IAM permission for sts:AssumeRole
  • setToContext are included for legacy support and should be avoided for performance and security reasons. See main documentation for best practices.

Sample usage

import middy from '@middy/core'
import sts from '@middy/sts'

const lambdaHandler = (event, context) => {
const response = {
statusCode: 200,
headers: {},
body: JSON.stringify({ message: 'hello world' })

return response

export const handler = middy()
fetchData: {
assumeRole: {
RoleArn: '...',
RoleSessionName: '' // optional


To exclude @aws-sdk add @aws-sdk/client-sts to the exclude list.