The AD FS Web Agent Authentication Service could not start. The authentication service has not been configured to run as ...

The AD FS Web Agent Authentication Service could not start. The authentication service has not been configured to run as a principal that has been granted the "Generate Security Audits" privilege (SeAuditPrivilege). 

Users will not be able to access protected resources until the authentication service can be restarted. 

User Action 
Either grant the AD FS authentication service principal the "Generate Security Audits" privilege or configure the authentication service to run as a principal that has already been granted the "Generate Security Audits" privilege. (For example, configure the authentication service to run as LocalSystem.)