message: add docs around assuming role for techdocs storage
diff: @@ -149,7 +149,7 @@ If the environment variables
  - `AWS_REGION`
  are set and can be used to access the bucket you created in step 2, they will be
  -used by the AWS SDK v3 Node.js client for authentication.
  +used by the AWS SDK v2 Node.js client for authentication.
  [Refer to the official documentation.](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/loading-node-credentials-environment.html)
  If the environment variables are missing, the AWS SDK tries to read the
  @@ -181,7 +181,7 @@ techdocs:
  ```
  Refer to the
  -[official AWS documentation for obtaining the credentials](https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/getting-your-credentials.html).
  +[official AWS documentation for obtaining the credentials](https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/getting-your-credentials.html).
  Note: If you are using Amazon EC2 instance to deploy Backstage, you do not need
  to obtain the access keys separately. They can be made available in the
  @@ -189,6 +189,27 @@ environment automatically by defining appropriate IAM role with access to the
  bucket. Read more
  [here](https://docs.aws.amazon.com/general/latest/gr/aws-access-keys-best-practices.html#use-roles).
  +**3c. Authentication using an assumed role** Users with multiple AWS accounts
  +may want to use a role for S3 storage that is in a different AWS account. Using
  +the `roleArn` parameter as seen below, you can instruct the TechDocs publisher
  +to assume a role before accessing S3.
  +
  +```yaml
  +techdocs:
  + publisher:
  + type: 'awsS3'
  + awsS3:
  + bucketName: 'name-of-techdocs-storage-bucket'
  + region:
  + $env: AWS_REGION
  + credentials:
  + roleArn: arn:aws:iam::123456789012:role/my-backstage-role
  +```
  +
  +Note: Assuming a role requires that primary credentials are already configured
  +at `AWS.config.credentials`. Read more about assuming roles
  +[here](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html)
  +
  **4. That's it!**
  Your Backstage app is now ready to use AWS S3 for TechDocs, to store and read
  