If you do not specify a user name, IAM determines the user name implicitly based on the AWS access key ID signing the request. Because this action works for access keys under the AWS account, you can use this API to manage root credentials even if the AWS account has no associated users.
For information about limits on the number of keys you can create, see Limitations on IAM Entities in Using AWS Identity and Access Management.To ensure the security of your AWS account, the secret access key is accessible only during key and user creation. You must save the key (for example, in a text file) if you want to be able to access it again. If a secret key is lost, you can delete the access keys for the associated user and then create new keys.
public CreateAccessKeyResponse CreateAccessKey()
The request was rejected because it attempted to create resources beyond the current
AWS account limits. The error message describes the limit exceeded.
The request was rejected because it referenced an entity that does not exist. The
error message describes the entity.