How to add tags to an existing IAM user via AWS CLI.

<pre lang="bash">aws iam tag-user \
--user-name john.doe \
--tags '{"Key": "Department", "Value": "Accounting"}'

Multiple tags.

<pre lang="bash">
aws iam tag-user \
--user-name john.doe \
--tags '[{"Key": "Department", "Value": "Accounting"},{"Key": "Manager", "Value": "jane.doe"}]'