Latest Cloudera Manager omit ldap_username_pattern entry from hue.ini build process.
Paste below into safety valve as a workaround.
[desktop] [[ldap]] ldap_username_pattern="username=,ou=user,dc=7979,dc=us"
P.S: Had some weird experience without ""
Hue with LDAP doesn't start up after Cloudera Manager upgrade
A Cloudera Manager upgrade drops ldap_username_pattern from hue.ini, so Hue with LDAP will not start until you put it back via safety valve.