[libmicrohttpd] Any suggestions on authentication for web clients to communicate with microhttp to manage multiple Linux servers with single /etc/shadow file

[lingweicai via libmicrohttpd]

Dear experts: 

I am to develop a web GUI with microhttpd as backend on a Linux Server as center node to manage/access multiple Linux servers as branches. I want to use one authentication system for all the servers, such as one set of /etc/passwd, /etc/shadow, /etc/group on center node by copying these file to branches nodes. Alternatively,  I am also consider to deploy LDAP ( have not deployed )  for web clients accessing center/branches hosts. 

I know cockpit can manage Linux server with users from web GUI as a system user of Linux, by using PAM. 

Any suggestions on my questions : 

1. which is better,  one user password system or LDAP ?

2. Is PAM is good choice ? 

Thanks,

Forrest Weicai Ling