zcl_jwt_generator.clas.abap

CLASS zcl_jwt_generator DEFINITION
  PUBLIC
  CREATE PUBLIC .

  PUBLIC SECTION.

    TYPES: BEGIN OF ty_jwt_header,
             alg TYPE string,
           END OF ty_jwt_header.

    TYPES: BEGIN OF ty_jwt_claim,
             iss TYPE string, "Issuer
             sub TYPE string, "Subject
             aud TYPE string, "Audience
             exp TYPE string, "Expiration Time
             nbf TYPE string, "Not Before
             iat TYPE string, "Issued At
             jti TYPE string, "JWT ID
           END OF ty_jwt_claim.

    METHODS generate_jwt
      IMPORTING jwt_header       TYPE ty_jwt_header
                jwt_claim        TYPE ty_jwt_claim
                ssf_info         TYPE ssfinfo
                ssf_format       TYPE ssfform  DEFAULT 'PKCS1-V1.5'
                ssf_hash_agrithm TYPE ssfhash  DEFAULT 'SHA256'
      RETURNING VALUE(jwt)       TYPE string
      RAISING   zcx_jwt_generator.

    METHODS base64url_encode
      IMPORTING unencoded        TYPE string
      RETURNING VALUE(base64url) TYPE string.

  PROTECTED SECTION.

  PRIVATE SECTION.

    TYPES:
      ty_tssfbin TYPE STANDARD TABLE OF ssfbin WITH KEY table_line WITHOUT FURTHER SECONDARY KEYS.

    METHODS string_to_binary_tab
      IMPORTING input_string       TYPE string
      RETURNING VALUE(output_bins) TYPE ty_tssfbin
      RAISING   zcx_jwt_generator.

    METHODS binary_tab_to_string
      IMPORTING input_bins           TYPE ty_tssfbin
                length               TYPE ssflen
      RETURNING VALUE(output_string) TYPE string
      RAISING   zcx_jwt_generator.

ENDCLASS.



CLASS zcl_jwt_generator IMPLEMENTATION.


  METHOD base64url_encode.
    base64url = cl_http_utility=>encode_base64( unencoded = unencoded ).
    REPLACE ALL OCCURRENCES OF '=' IN base64url WITH ''.
    REPLACE ALL OCCURRENCES OF '+' IN base64url WITH '-'.
    REPLACE ALL OCCURRENCES OF '/' IN base64url WITH '_'.
  ENDMETHOD.


  METHOD binary_tab_to_string.
    CALL FUNCTION 'SCMS_BINARY_TO_STRING'
      EXPORTING
        input_length = length
        encoding     = '4110'
      IMPORTING
        text_buffer  = output_string
      TABLES
        binary_tab   = input_bins
      EXCEPTIONS
        failed       = 1
        OTHERS       = 2.
    IF sy-subrc <> 0.
      RAISE EXCEPTION TYPE zcx_jwt_generator USING MESSAGE.
    ENDIF.
  ENDMETHOD.


  METHOD generate_jwt.

    DATA input_bins TYPE STANDARD TABLE OF ssfbin.
    DATA output_bins TYPE STANDARD TABLE OF ssfbin.
    DATA input_length TYPE ssflen.
    DATA output_length TYPE ssflen.
    DATA output_crc TYPE ssfreturn.
    DATA signers TYPE STANDARD TABLE OF ssfinfo.
    DATA: jwt_claim_json       TYPE string,
          jwt_header_json      TYPE string,
          jwt_header_base64url TYPE string,
          jwt_claim_base64url  TYPE string.
    DATA input_base64url TYPE string.
    DATA: signature           TYPE string,
          signature_base64url TYPE string.


    jwt_header_json = /ui2/cl_json=>serialize(
      compress = abap_true
      data  = jwt_header
      pretty_name = /ui2/cl_json=>pretty_mode-low_case    ).

    jwt_claim_json = /ui2/cl_json=>serialize(
      compress = abap_true
      data  = jwt_claim
      pretty_name = /ui2/cl_json=>pretty_mode-low_case  ).


    jwt_header_base64url = base64url_encode( jwt_header_json ).
    jwt_claim_base64url = base64url_encode( jwt_claim_json ).


    input_base64url = |{ jwt_header_base64url }.{ jwt_claim_base64url }|.
    input_length = strlen( input_base64url ).

    input_bins = string_to_binary_tab( input_string = input_base64url ).


    APPEND ssf_info TO signers.

    CALL FUNCTION 'SSF_KRN_SIGN'
      EXPORTING
        str_format                   = ssf_format
        b_inc_certs                  = abap_false
        b_detached                   = abap_false
        b_inenc                      = abap_false
        ostr_input_data_l            = input_length
        str_hashalg                  = ssf_hash_agrithm
      IMPORTING
        ostr_signed_data_l           = output_length
        crc                          = output_crc    " SSF Return code
      TABLES
        ostr_input_data              = input_bins
        signer                       = signers
        ostr_signed_data             = output_bins
      EXCEPTIONS
        ssf_krn_error                = 1
        ssf_krn_noop                 = 2
        ssf_krn_nomemory             = 3
        ssf_krn_opinv                = 4
        ssf_krn_nossflib             = 5
        ssf_krn_signer_list_error    = 6
        ssf_krn_input_data_error     = 7
        ssf_krn_invalid_par          = 8
        ssf_krn_invalid_parlen       = 9
        ssf_fb_input_parameter_error = 10.
    IF sy-subrc <> 0.
      RAISE EXCEPTION TYPE zcx_jwt_generator USING MESSAGE.
    ENDIF.

    signature = binary_tab_to_string( input_bins = output_bins
                                      length  = output_length ).

    signature_base64url = base64url_encode( signature ).

    jwt = |{ input_base64url }.{ signature_base64url }|.

  ENDMETHOD.


  METHOD string_to_binary_tab.
    DATA lv_xstring TYPE xstring.

    CALL FUNCTION 'SCMS_STRING_TO_XSTRING'
      EXPORTING
        text     = input_string
        encoding = '4110'
      IMPORTING
        buffer   = lv_xstring
      EXCEPTIONS
        failed   = 1
        OTHERS   = 2.
    IF sy-subrc <> 0.
      RAISE EXCEPTION TYPE zcx_jwt_generator USING MESSAGE.
    ENDIF.

    CALL FUNCTION 'SCMS_XSTRING_TO_BINARY'
      EXPORTING
        buffer     = lv_xstring
      TABLES
        binary_tab = output_bins.
    IF sy-subrc <> 0.
      RAISE EXCEPTION TYPE zcx_jwt_generator USING MESSAGE.
    ENDIF.
  ENDMETHOD.
ENDCLASS.