Description of problem: libu2f-host is responsible for issuing u2f queries to attached tokens and waiting for user response. However, if a "check-only" authentication request[0] is presented, the sleep logic still delays for a full second before returning the results when no delay is necessary. This was fixed in PR#97[1], which is included in relase v1.1.6 in the upstream.

This issue was discovered because pam-u2f 1.0.6 or later issues a check-only authentication as a security measure to avoid leaking information about the authentication stack in certain scenarios. Ergo, if using pam-u2f 1.0.6 or later (1.0.7 contains a workaround), every u2f authentication takes a 1-second delay.

[0] - 
https://fidoalliance.org/specs/fido-u2f-v1.0-nfc-bt-amendment-20150514/fido-u2f-raw-message-formats.html
[1] - https://github.com/Yubico/libu2f-host/pull/97


Version-Release number of selected component (if applicable): 1.1.3-3.fc27


How reproducible: Always


Steps to Reproduce:
1. Install and configure pam-u2f 1.0.6 or later.
2. Observe that every u2f authentication sleeps for a second before requesting user input.

Actual results:

There is a one-second delay between the previous pam module and the u2f user-presence authentication. 

Expected results: 

User-presence authentication should begin immediately.

Additional info:

pam-u2f 1.0.7 contains an option to avoid this early detection as either a workaround for this issue, or for hypothetical tokens that do not tolerate it. Either way, there's no reason for the delay in a check-only authentication.