Correct URL for assertion export

[Rainer Hoerbe]

I want to export the assertion using this URL:

http://127.0.0.1:8080/Shibboleth.sso/GetAssertion?key=_8bc8dd882335a52494d208fab7966ab0&ID=01

As result I get HTTP 500 "Assertion Lookup Failed". There is no corresponding "assertion (%s) not found in session (%s)" message in the log.

I can get past session validation, as key=xxx would result in
2017-12-12 07:47:26 ERROR Shibboleth.AssertionLookup [2]: valid session (xx) not found for assertion lookup

Are the URL parameters correct? The documentation how to query the AssertionExport handler was not clear to me:
https://wiki.shibboleth.net/confluence/display/SHIB2/NativeSPAssertionExport

- Rainer