wpa_supplicant.conf permission
On my phone permissions and ownership looks like:

ls -las /data/misc/wifi/
12 drwxrwx---  4 wifi   wifi    4096 2017-08-14 16:30 .
 8 drwxrwx--t 39 system misc    4096 2017-08-12 20:54 ..
 8 -rw-rw----  1 system wifi      21 2017-08-14 16:30 entropy.bin
48 -rw-rw----  1 system wifi   43098 2017-08-12 22:36 hostapd.conf
 8 -rw-------  1 system system  3136 2017-08-12 23:27 ipconfig.txt
52 -rw-------  1 system system 44517 2017-08-14 16:30 networkHistory.txt
 4 -rw-rw----  1 wifi   wifi     186 2017-08-14 16:30 p2p_supplicant.conf
12 drwxrwx---  2 wifi   wifi    4096 2017-08-14 16:30 sockets
 8 -rw-------  1 system system    20 2017-08-12 22:36 softap.conf
12 drwxrwx---  2 wifi   wifi    4096 1970-01-10 00:56 wpa_supplicant
16 -rw-rw----  1 wifi   wifi   10957 2017-08-14 16:30 wpa_supplicant.conf