I am trying to verify the user identity on my application using a certificate / identity that the user has stored by opening a .cer / .p12 attached to an email. The certificate
You talked about the Security framework already, but did you try the following functions in the doc?
I personally never tried/had to do this myself, but anyway it seems that there are some functions like SecCertificateCreateWithData
in the framework, so you should be able to build a SecCertificateRef
from some NSData/CFDataRef… data which is the content of your mail attachment.
From there you may use it as any other certificate using the other functions (like you would do for a certificate extracted from the Keychain)
Well this is only a guess after simply reading the documentation but let's give it a try as the doc seems to indicate it is the way to go.