How to reach web service from CRM web client

Hello everybody, I am enhancing a CRM Case:

app component     CRM-CM
view:                    CRMCMP_CMG/Detail
object type          CRM_CMG

I have to call a web service and set the result to my fields.
I have tested the WS and it works:

in SAP GUI it asks me for user and password then DO retrieves result.. 
in CRM web client it does Not ask anithing so I am not reaching the WS and no result,

this is code in an button event in my Case
***call to Function that calls the WS

  CALL FUNCTION 'ZBSIGNED'
    IMPORTING
      e_value        = l_value
    EXCEPTIONS
      not_found      = 1
      OTHERS         = 2.

***set field value

  CALL METHOD me->typed_context->detail->if_bsp_model_binding~set_attribute
  EXPORTING
    attribute_path = 'EXT.ZZFLD000052'
    value          = l_value.

I made my function with code like this, plus an export parameter added to my function.
https://www.sdn.sap.com/irj/scn/index?rid=/library/uuid/802edea6-274e-2e10-fd95-e5e1a8bc0892&overridelayout=true

Please help, Thank you