Revert "Revert "ADPKeyAuthHelper needs to still return a string even if there's no cert""
Revert "Revert "ADPKeyAuthHelper needs to still return a string even if there's no cert""

This reverts commit 3e1020fe5ef9591b1976db8f8faaec96e5b2d652.

AzureAD/azure-activedirectory-library-for-objc,msintuneappsdk/azure-activedirectory-library-for-objc,AzureAD/azure-activedirectory-library-for-objc,AzureAD/azure-activedirectory-library-for-objc,msintuneappsdk/azure-activedirectory-library-for-objc,AzureAD/azure-activedirectory-library-for-objc,AzureAD/azure-activedirectory-library-for-objc,msftberlin/azure-activedirectory-library-for-objc,msftberlin/azure-activedirectory-library-for-objc