How to use cl_http_client to access a SSL url.

I want to access Salesforce url.

When I use this object to access http url,it work fine.

but for https, this not work.

ERROR  HTTP_COMMUNICATION_FAILURE

My ABAP code like below.

DATA: CL type ref to if_http_client.

CALL METHOD cl_http_client=>create_by_url
EXPORTING
url = 'https://na17.salesforce.com/services/data/'
SSL_ID = 'DFAULT'
IMPORTING
client = cl
EXCEPTIONS
OTHERS = 1.
call method CL->send
exceptions
HTTP_COMMUNICATION_FAILURE = 1
HTTP_INVALID_STATE = 2
HTTP_PROCESSING_FAILED = 3
HTTP_INVALID_TIMEOUT = 4.


call method CL->receive
exceptions
HTTP_COMMUNICATION_FAILURE = 1.

DATA: S TYPE STRING,
       sub_string type string.

  s =  cl->RESPONSE->get_cdata( ).

The error htm like below.

500 Native SSL error

########## ############

Should I get a CA certificate from salesforce and upload into sap sever in trust?

Would you please tell me how to make it work ,step by step?becuase I lack basis knowledge and now has no basis resource.