FMS 4.5.1 - How to implement client authentication?

yes, see here:

http://httpd.apache.org/docs/2.0/howto/auth.html

under "getting it working"

the idea is to use basicauth in hls and hds location(s) in httpd.conf

that way, the stream would be accessible via this url:

http://user:pass@name-of-the-server/..../..m3u8

but then, the username and password would be easily sniffed so you should install server certificate, set listen 443 in the same conf

and use https instead of http so that username and password are sent encrypted

I haven't found easier solution than this for hls/hds authentication but still not 100% sure if it will work inside iOS aplication - i see no reason why it should not...

for rtmp, as i already said, you could implent anything you want in asc on server side and inside your player, some coding in AS needed for this, you do not need to call webservices per se, i do not have a concrete example but i'm sure that one can be found by serching this forum or related sites like fmsguru...

for the record, adobe engineers here are way more experienced and may have better ideas or prove me wrong...