FreeRDP requires OpenSSL libraries for building but they are not part of the iOS SDK and therefore they need to be pre-build manually.
There are various versions and builds of static OpenSSL libraries floating around like iOSPorts.
At the time of writing we have tested and used a small script (OpenSSL-DownloadAndBuild.command) that downloads and builds armv7, armv7s and i386 versions of the OpenSSL 1.0.0e libraries.
If you don't care about modifying the OpenSSL build you can run the following command in the FreeRDP root directory:
* the platform for which to build iFreeRDP. OS compiles for iOS devices (using armv7 and armv7s ABIs) and SIMULATOR compiles for the iOS Simulator (i386)
CMAKE_IOS_DEVELOPER_ROOT (used by toolchain file)
* absolute path to the iOS developer platform (i.e. /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer) the toolchain file will usually auto-detect the correct Developer platform depending on IOS_PLATFORM
CMAKE_IOS_SDK_ROOT (used by toolchain file)
* absolute path to the iOS SDK (i.e. /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk) the toolchain file will usually auto-detect the correct SDK, depending on IOS_PLATFORM
FREERDP_IOS_EXTERNAL_SSL_PATH (used by FindOpenSSL)
* absolut root path to the pre-built static OpenSSL libraries