Retrieving username/password from HTTP Authentication in webservice

I have a webservice which receives a post with the user name/password in the headers:
POST /reporting/test.asmx/user_reply? HTTP/1.1

Authorization: Basic Z2lsbGlhbjpnaWxsaWFu

Host: 10.1.1.88:666

Pragma: no-cache

Accept: */*

Content-Length: 141

Content-Type: application/x-www-form-urlencoded
id=3130890&msg=8d62409c2202b238ce09be5a09254607
HTTP/1.1 100 Continue

Server: Microsoft-IIS/5.1

Date: Wed, 19 Nov 2008 23:16:08 GMT

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I can retrieve the 'id' and 'msg' values from the query string by doing something like
string id = this.Context.Request.QueryString["id"];
but i don't know how to retrieve the user name/password values from the post.

Can some please help ?
 
 
 
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