Created attachment 32755 [details]
patch

Hi,

I've created a new environment variable in order to test for an extended key usage into a certificate. Like clientAuth on a client certificate authentication for instance. This variable can then be used on a Require directive as follow : 

Require expr %{SSL_CLIENT_EXT_KEYUSAGE_clientAuth} == "true"

Format of the variable name is as follow : 

SSL_{CLIENT|SERVER}_EXT_KEYUSAGE_purpose 

Where purpose is either a shortname ( serverAuth, clientAuth etc...) or an oid. Shortname are case insensitive and '.' on oid must be replace with '_'.
Here is some valid examples : 

SSL_CLIENT_EXT_KEYUSAGE_clientAuth 
SSL_SERVER_EXT_KEYUSAGE_SERVERAUTH
SSL_CLIENT_EXT_KEYUSAGE_1_3_6_1_5_5_7_3_2

We may improve the comparison of oid by checking each number one by one instead of converting both var (replace '_' by '.') and obj (convert into char*) and do a strcmp. But I'm not sure if openssl offers another way to get oid other than OBJ_obj2txt(). 

We may also add the export of all the purpose as variable when +StdEnvVars is set on SSLOptions.

Please feel free to give me any feedback about code, patch, documentation etc...