How to restrict special characters in user name

Summary:

While creating user in cloud application, system is allowing special characters in user name.

Could you please advice, how to restrict special characters in username DFF.

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Code Snippet (add any code snippets that support your topic, if applicable):

Please find the navigation steps to "Manage users".

Setup and maintenance-choose offerings/setup as "Financials"- search with task name "Manage Users"-Click on (+) or search with user name if already user exist.