Friday, 4 August 2017

Regarding cookie manipulation in CL_HTTP_CLIENT to avoid CSRF token validation failure issue

Recently I meet with this cookie issue so I document it as a blog in case any other guys might meet with the same problem.

I am trying to create some Opportunity transaction data by consuming OData service via CL_HTTP_CLIENT. Since this is a update operation which needs to be finished by HTTP POST, so a CSRF token is needed in this HTTP post. Let’s first have a look what is a typical scenario running in Chrome extension postman:

1. Perform a HTTP get operation with header field x-csrf-token = fetch to get a valid CSRF token from http response header field.

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

2. launch a HTTP post request using the CSRF token got from previous step,

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

And a new opportunity could successfully be created in postman:

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

However, when I implement the above mentioned scenario in ABAP, I meet with trouble. Instead of the expected successful creation message, I always get the error message “CSRF token validation failed”.

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

Issue trouble shooting


Let’s go back to postman scenario. Although it seems only the header field x-csrf-token is specified in http request, however there is another field cookie which is added to http request under the hood.

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

We could get this cookie field from previous HTTP get request which is responsible for CSRF token retrieve:

ABAP Development, ABAP Connectivity, ABAP Testing and Analysis

It means in ABAP implementation, we need to first retrieve BOTH CSRF token and cookie field from the first HTTP GET request, and then added these two fields to the request of second HTTP POST request which actually performs the opportunity creation.

I just added the complete source code of my implementation here and feel free to reuse it.
The ABAP report to create Opportunity by consuming OData service:

zcl_odata_tool=>get_csrf_token_and_cookie( IMPORTING et_cookies = DATA(lt_cookie)
                                                     ev_token = DATA(lv_token)  ).
zcl_odata_tool=>create_opp( iv_token = lv_token it_cookies = lt_cookie ).

Source code for ZCL_ODATA_TOOL:


CLASS zcl_odata_tool DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC .
  PUBLIC SECTION.
    CLASS-METHODS get_csrf_token_and_cookie
      EXPORTING
        !et_cookies TYPE tihttpcki
        !ev_token TYPE string .
    CLASS-METHODS create_opp
      IMPORTING
        !iv_token TYPE string
        !it_cookies TYPE tihttpcki .
  PROTECTED SECTION.
  PRIVATE SECTION.
ENDCLASS.
CLASS ZCL_ODATA_TOOL IMPLEMENTATION.
  METHOD create_opp.
    DEFINE insert_line.
      lv_body = lv_body && &1.
      lv_body = lv_body && cl_abap_char_utilities=>newline.
    END-OF-DEFINITION.

    DATA:lo_http_client TYPE REF TO if_http_client,
             lv_status      TYPE i,
             lt_fields      TYPE tihttpnvp,
             lv_sysubrc     TYPE sysubrc.

    CALL METHOD cl_http_client=>create_by_url
      EXPORTING
        url                = 'https://<your C4C host>/sap/c4c/odata/v1/c4codata/$batch'
      IMPORTING
        client             = lo_http_client
      EXCEPTIONS
        argument_not_found = 1
        plugin_not_active  = 2
        internal_error     = 3
        OTHERS             = 4.

    ASSERT sy-subrc = 0.
    lo_http_client->propertytype_accept_cookie = if_http_client=>co_enabled.

    CALL METHOD lo_http_client->request->set_method( if_http_request=>co_request_method_post ).

    lo_http_client->request->set_header_field( name = 'Content-Type' value = 'multipart/mixed; boundary=batch_1' ).
    lo_http_client->request->set_header_field( name = 'x-csrf-token' value = iv_token ).
    lo_http_client->request->set_header_field( name = 'Authorization' value = 'your basic authentication code' ).
    LOOP AT it_cookies ASSIGNING FIELD-SYMBOL(<cookie>).
      lo_http_client->request->set_cookie( name = <cookie>-name
                                           value = <cookie>-value ).
    ENDLOOP.
    DATA: lv_body TYPE string.

    insert_line '--batch_1'.
    insert_line 'Content-Type: multipart/mixed; boundary=changeset_1'.
    lv_body = lv_body && cl_abap_char_utilities=>cr_lf.
*
    insert_line '--changeset_1'.
    insert_line 'Content-Type: application/http'.
    insert_line 'Content-Transfer-Encoding: binary'.
    lv_body = lv_body && cl_abap_char_utilities=>cr_lf.

    insert_line 'POST OpportunityCollection HTTP/1.1'.
    insert_line 'Content-Length: 5000'.
    insert_line 'Accept: application/json'.
    insert_line 'Content-Type: application/json'.

    lv_body = lv_body && cl_abap_char_utilities=>cr_lf.
    insert_line '{'.
    insert_line '"AccountID": "8000018122",'.
    insert_line '"OwnerID": "8000018122",'.
    insert_line `"Name": {"content": "Testing ticket creation via OData Jerry1"}`.
    insert_line '}'.
    insert_line '--changeset_1--'.
    lv_body = lv_body && cl_abap_char_utilities=>cr_lf.
    insert_line '--batch_1--'.

    lo_http_client->request->set_cdata( data = lv_body ).
    CALL METHOD lo_http_client->send
      EXCEPTIONS
        http_communication_failure = 1
        http_invalid_state         = 2
        http_processing_failed     = 3.

    ASSERT sy-subrc = 0.

    CALL METHOD lo_http_client->receive
      EXCEPTIONS
        http_communication_failure = 1
        http_invalid_state         = 2
        http_processing_failed     = 3.

    IF sy-subrc <> 0.
      CALL METHOD lo_http_client->get_last_error
        IMPORTING
          code    = lv_sysubrc
          message = DATA(ev_message).
      WRITE: / 'error occurred during receive data' COLOR COL_NEGATIVE.
      RETURN.
    ENDIF.
    DATA(lv_json) = lo_http_client->response->get_cdata( ).
    WRITE:/ lv_json.
  ENDMETHOD.

  METHOD get_csrf_token_and_cookie.
    DATA:  lo_http_client TYPE REF TO if_http_client,
           lv_status      TYPE i,
           lt_fields      TYPE tihttpnvp,
           lv_sysubrc     TYPE sysubrc.

    CALL METHOD cl_http_client=>create_by_url
      EXPORTING
        url                = 'https://<your C4C host>/sap/c4c/odata/v1/c4codata/'
      IMPORTING
        client             = lo_http_client
      EXCEPTIONS
        argument_not_found = 1
        plugin_not_active  = 2
        internal_error     = 3
        OTHERS             = 4.

    ASSERT sy-subrc = 0.
    lo_http_client->propertytype_accept_cookie = if_http_client=>co_enabled.

    CALL METHOD lo_http_client->request->set_method( if_http_request=>co_request_method_get ).
    lo_http_client->request->set_header_field( name = 'x-csrf-token' value = 'Fetch' ).
    lo_http_client->request->set_header_field( name = 'Accept' value = 'application/json' ).
    lo_http_client->request->set_header_field( name = 'Content-Type' value = 'application/json' ).
    lo_http_client->request->set_header_field( name = 'Authorization' value = 'Your basic authentication' ).

    CALL METHOD lo_http_client->send
      EXCEPTIONS
        http_communication_failure = 1
        http_invalid_state         = 2
        http_processing_failed     = 3.

    ASSERT sy-subrc = 0.

    CALL METHOD lo_http_client->receive
      EXCEPTIONS
        http_communication_failure = 1
        http_invalid_state         = 2
        http_processing_failed     = 3.

    IF sy-subrc <> 0.
      CALL METHOD lo_http_client->get_last_error
        IMPORTING
          code    = lv_sysubrc
          message = DATA(ev_message).
      WRITE: / 'Error when getting token:', ev_message.
      RETURN.
    ENDIF.

    lo_http_client->response->get_header_fields( CHANGING fields = lt_fields ).

    READ TABLE lt_fields ASSIGNING FIELD-SYMBOL(<field>) WITH KEY name = 'x-csrf-token'.
    ev_token = <field>-value.

    lo_http_client->response->get_cookies( CHANGING cookies = et_cookies ).
    lo_http_client->close( ).

  ENDMETHOD.
ENDCLASS.

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