Currently passing an invalid Basic auth header (random string base64 encoded) would result in an exception being raised due to a username, password = auth_header.split().
Similary passing a `Digest` authentication type would result in an exception as there is no :.
Thirdly passing invalid base64 encoded UTF-8 code sequences would result in exceptions as this issue (#1424).
I added code to check explicitly that we are doing basic authentication then by checking the number of entries returned by the split.
I also added exception handling for invalid UTF-8 code sequence exceptions.
Tested with a fuzzer.
Tested with valid and invalid credentials.
This fixes#1424.
CSRF has been initialized *before* the app config was fully read. That
made it impossible to configure CSRF properly. Moved the CSRF init into
the routes module, and switched from programmatic to decorated
exemptions. GET routes don't need to be exempted because they are by
default.
