Where do I enter the username and password on the rest server

I have windows rest server working with TSparkleHttpSysDispatcher, TXDataServer, TAureliusConnection and firedac.

I have enabled the middleware srvBasicAuth in TXDataServer.

Where/How do I specify the username and password on the server?

You can check the Basic Authentication middleware documentation here:

https://doc.tmssoftware.com/biz/sparkle/guide/middleware.html#basic-authentication-middleware

Basically what you have to do is provide an event handler that checks for user name and password and, if valid, return a IUserIdentity interface.

The documentation shows the use of the middleware directly from code, but if you are using it at design-time, just use the OnAuthenticate event, the idea is the same.