The Simple Certificate Enrollment Protocol (SCEP, rhymes with “step”) is an X.509 certificate enrollment protocol that uses PKCS#7 and PKCS#10 over HTTP.
Apple uses SCEP for "over the air" certificate enrollment on the iPhone:
For more information about SCEP and the iPhone, perform this google search:
Simple Certificate Enrollment Protocol iphone site:apple.com
On the iPhone, the SCEP protocol is bootstrapped by typing a username/password into a Safari browser window (which immediately suggests that federated access may be possible).
An interesting application of SCEP: