Remote Phonebook provision tXXp phones HTTP 401 error

Hello,

When I tried to download remote phonebook from directory with htaccess. The phone try with empty http username (don't authenticate), and return with 401 HTTP error.

Here's the apache log:
x.x.x.x - - [18/Aug/2015:10:26:27 +0000] "GET /dir_to_phonebook/phonebookgenerator.php?mac=00156529fbee HTTP/1.1" 401 653 "-" "Yealink SIP-T26P 6.73.0.50 00:15:65:29:fb:ee"


x.x.x.x - "" [18/Aug/2015:10:26:27 +0000] "GET /dir_to_phonebook/phonebookgenerator.php?mac=00156529fbee HTTP/1.1" 401 652 "-" "Yealink SIP-T26P 6.73.0.50 00:15:65:29:fb:ee"

apache (Server version: Apache/2.4.7 (Ubuntu)) config:

<Directory dir_to_phonebook>
Options Indexes FollowSymLinks MultiViews
AllowOverride all
Require env let_me_in
</Directory>

htaccess:
AuthType Basic
AuthName "For Authorized Personal Only"
AuthUserFile /etc/apache2/.htpasswd
Require user user_to_authenticate