I don’t have any suggestions, but I’m having what seems to be the same problem, also using Apache (2.4.19), mpm_event, and php-fpm (though php 7.2, not 7.0)–although I’m seeing it when running under FreeBSD 11.1. Nothing is written to nextcloud.log even when set at log level 1 (info), but when I set the log level to debug, I get this:
{"reqId":"xKofwVyOupn2Y5ypWNqA","level":0,"time":"2018-03-23T11:26:28-04:00","remoteAddr":"192.168.3.2","user":"--","app":"webdav","method":"PROPFIND","url":"\/remote.php\/webdav\/","message":"Exception:
{\"Exception\":\"Sabre\\\\DAV\\\\Exception\\\\NotAuthenticated\",\"Message\":\"No
'Authorization: Basic' header found. Either the client didn't send one,
or the server is misconfigured, No 'Authorization: Bearer' header found.
Either the client didn't send one, or the server is
mis-configured\",\"Code\":0,\"Trace\":\"#0 [internal function]:
Sabre\\\\DAV\\\\Auth\\\\Plugin->beforeMethod(Object(Sabre\\\\HTTP\\\\Request),
Object(Sabre\\\\HTTP\\\\Response))\\n#1
\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/3rdparty\\\/sabre\\\/event\\\/lib\\\/EventEmitterTrait.php(105):
call_user_func_array(Array, Array)\\n#2
\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/3rdparty\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Server.php(466):
Sabre\\\\Event\\\\EventEmitter->emit('beforeMethod', Array)\\n#3
\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/3rdparty\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Server.php(254):
Sabre\\\\DAV\\\\Server->invokeMethod(Object(Sabre\\\\HTTP\\\\Request),
Object(Sabre\\\\HTTP\\\\Response))\\n#4
\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/apps\\\/dav\\\/appinfo\\\/v1\\\/webdav.php(80):
Sabre\\\\DAV\\\\Server->exec()\\n#5
\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/remote.php(164):
require_once('\\\/usr\\\/local\\\/www\\\/...')\\n#6
{main}\",\"File\":\"\\\/usr\\\/local\\\/www\\\/apache24\\\/data\\\/nextcloud\\\/3rdparty\\\/sabre\\\/dav\\\/lib\\\/DAV\\\/Auth\\\/Plugin.php\",\"Line\":168}","userAgent":"Mozilla\/5.0
(Macintosh) mirall\/2.3.3 (build 84) (Nextcloud)","version":"13.0.1.1"}
The username and password entered are correct; if I enter an incorrect password, I get an authentication failure.