If you do not specify a user name, IAM determines the user name
implicitly based on the AWS access key ID signing the request. This
operation works for access keys under the AWS account. Consequently, you
can use this operation to manage AWS account root user credentials. This
is true 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 the IAM User Guide.
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.