The debug build of some code utilizing SFHFKeychainUtils that is working without complaint on the mac which I'm developing on is triggering an error on another mac:
The code makes use of the following methods provided by SFHFKeychainUtils:
+[SFHFKeychainUtils getPasswordForUsername:andServiceName:accessGroup:error:]
+[SFHFKeychainUtils storeUsername:andPassword:forServiceName:accessGroup:updateExisting:updateExisting:error:]
A password is added for a username using +[SFHFKeychainUtils storeUsername:andPassword:forServiceName:accessGroup:updateExisting:updateExisting:error:]. Some time later, an attempt is made to retrieve the password using +[SFHFKeychainUtils getPasswordForUsername:andServiceName:accessGroup:error:]. However, this method is returning the error; its domain is SFHFKeychainUtilsErrorDomain and its code is -25293 (so it is errSecAuthFailed). This error is only returned when a password is in fact stored in the keychain (or at least when it is visible from Keychain Access).
Why is this taking place?
The problem is a lack of code signing. Code signing is required in order for the second machine to access the keychain. The fix was to enable code signing for the debug build.