Use page request parameters to derive the filter value from the current Web Part Page HTTP request context:
The Page Request / URL Filter is capable of parsing various request parameter formats. Observe how the Matching URL format example area changes immediately in response to your changes to see exactly what kind of input the filter expects with the current setup. (In principle this applies even when using a request mode other than URL query string.)
If the specified request parameter bundles multiple name-value pairs in a single
parameter value, an individual sub-parameter value can be derived by entering
the sub-parameter name, if the parameter value conforms to the syntax that is
also used by Microsoft Office SharePoint Server Advanced Search forms / results pages