Authentication of users connecting to a LAN via an EX switch can be performed via 802.1X, MAC RADIUS, or captive portal. Users accessing the EX switch for management purposes can be authenticated via RADIUS, TACACS+ and local password. 

However, authentication via LDAP is not supported.

• The LDAP option is not available to users that want to connect to a LAN via an QFX switch.
• When configuring user access to the switch, the LDAP option is not available:

Switch# set system authentication-order ?
Possible completions:
  [                    Open a set of values
  password             Traditional password authentication
  radius               Remote Authentication Dial-In User Service
  tacplus              TACACS+ authentication services

We checked in path finder and we could see that the LDAP is not supported in Qfx device.

As per the feature support document the LDAP authentication support in SRX platforms.

https://apps.juniper.net/feature-explorer/search-features.html

Hence, its not supported in QFX device.