Several OpenSSL structures can have application specific data attached to them.
These functions are used internally by OpenSSL to manipulate application
specific data attached to a specific structure.
These functions should only be used by applications to manipulate
CRYPTO_EX_DATA structures passed to the new_func(), free_func() and
dup_func() callbacks: as passed to RSA_get_ex_new_index() for example.
CRYPTO_set_ex_data() is used to set application specific data, the data is
supplied in the arg parameter and its precise meaning is up to the
CRYPTO_get_ex_data() is used to retrieve application specific data. The data
is returned to the application, this will be the same value as supplied to
a previous CRYPTO_set_ex_data() call.