You can use AssumeRole to enable new or existing database users to connect to the Redshift database. You can use an IAM role configured with required trust policies to generate temporary security credentials to access Amazon Redshift. You can enable IAM users or define an EC2 instance to assume an IAM role to access Redshift.

Additionally, you can also enable cross-account access where the Redshift cluster, S3 bucket, and Redshift IAM role ARN are in one account and the IAM users or the EC2 role are in a different account. In this scenario, you need to configure the user accounts to assume the role in the Redshift cluster account.