How do I pass a portal username to an ASP page?

You can pass any available user attributes to custom applications written in PHP, JSP, ASP, Perl, etc. as HTTP GET parameters on requests from the Web Proxy Channel.

For example, a Web Proxy channel configured like this...

Channel Publishing Parameter	Value
Application URI	https://someserver/somescript.asp
Default IPerson Attributes to Pass	username
Restrict IPerson Attributes Passing to These	username

...will issue an HTTP GET request like

https://someserver/somescript.asp?username=apetro

and present the results of that request in the channel.