The user needs to do Radius authentication from a custom HTTP header transferring the username and password. They are able to use the example from the Doc page  using Basic Authentication. However, the user needs to extract the credentials from a custom HTTP header. When trying to use "Require XPath Credentials" , the Radius assertion logs that "No credentials were found" although the "Require XPath Credentials" assertion passed with the given input.
How can we pass custom string values as username/password values to the Radius assertion?
 Wiki page
 Require XPath Credentials
The attached sample policy that authenticates users with credentials specified in an HTML form. A policy author will only need to change the "Set Context Variable" assertions to reflect the name of the HTML form fields that contain the username and password.
The policy can be simplified to only use the "Require XPath Credentials" assertion to point to the variable that refers to the HTML form fields but the policy provided simplifies the process.