(PureBasic) Get E-way Bill System Access Token

Sends a request to get an E-way bill system access token.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkPublicKey.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkPrng.pb"
IncludeFile "CkHttpResponse.pb"
IncludeFile "CkFileAccess.pb"
IncludeFile "CkHttp.pb"
IncludeFile "CkCrypt2.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkRsa.pb"
IncludeFile "CkBinData.pb"

Procedure ChilkatExample()

    ;  This example requires the Chilkat API to have been previously unlocked.
    ;  See Global Unlock Sample for sample code.

    ;  First load the public key provided by the E-way bill System
    pubkey.i = CkPublicKey::ckCreate()
    If pubkey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkPublicKey::ckLoadFromFile(pubkey,"qa_data/pem/eway_publickey.pem")
    If success <> 1
        Debug CkPublicKey::ckLastErrorText(pubkey)
        CkPublicKey::ckDispose(pubkey)
        ProcedureReturn
    EndIf

    ;  Encrypt the password using the RSA public key provided by eway..
    password.s = "my_wepgst_password"
    rsa.i = CkRsa::ckCreate()
    If rsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkRsa::setCkCharset(rsa, "utf-8")
    CkRsa::setCkEncodingMode(rsa, "base64")

    success = CkRsa::ckImportPublicKeyObj(rsa,pubkey)
    If success <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ;  Returns the encrypted password as base64 (because the EncodingMode = "base64")
    encPassword.s = CkRsa::ckEncryptStringENC(rsa,password,0)
    If CkRsa::ckLastMethodSuccess(rsa) <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ;  Generate a random app_key.  This should be 32 bytes (us-ascii chars)
    ;  We need 32 bytes because we'll be doing 256-bit AES ECB encryption, and 32 bytes = 256 bits.
    prng.i = CkPrng::ckCreate()
    If prng.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  Generate a random string containing some numbers, uppercase, and lowercase.
    app_key.s = CkPrng::ckRandomString(prng,32,1,1,1)

    Debug "app_key = " + app_key

    ;  RSA encrypt the app_key.
    encAppKey.s = CkRsa::ckEncryptStringENC(rsa,app_key,0)
    If CkRsa::ckLastMethodSuccess(rsa) <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        CkPrng::ckDispose(prng)
        ProcedureReturn
    EndIf

    ;  Prepare the JSON body for the HTTP POST that gets the access token.
    jsonBody.i = CkJsonObject::ckCreate()
    If jsonBody.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckUpdateString(jsonBody,"action","ACCESSTOKEN")
    ;  Use your username instead of "09ABDC24212B1FK".
    CkJsonObject::ckUpdateString(jsonBody,"username","09ABDC24212B1FK")
    CkJsonObject::ckUpdateString(jsonBody,"password",encPassword)
    CkJsonObject::ckUpdateString(jsonBody,"app_key",encAppKey)

    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  Add required headers.
    ;  Use your ewb-user-id instead of "03AEXPR16A9M010"
    CkHttp::ckSetRequestHeader(http,"ewb-user-id","03AEXPR16A9M010")
    ;  The Gstin should be the same as the username in the jsonBody above.
    CkHttp::ckSetRequestHeader(http,"Gstin","09ABDC24212B1FK")
    CkHttp::setCkAccept(http, "application/json")

    ;  POST the JSON...
    resp.i = CkHttp::ckPostJson2(http,"http://ewb.wepgst.com/api/Authenticate","application/json",CkJsonObject::ckEmit(jsonBody))
    If CkHttp::ckLastMethodSuccess(http) <> 1
        Debug CkHttp::ckLastErrorText(http)
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        CkPrng::ckDispose(prng)
        CkJsonObject::ckDispose(jsonBody)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    respStatusCode.i = CkHttpResponse::ckStatusCode(resp)
    Debug "response status code =" + Str(respStatusCode)
    Debug "response body:"
    Debug CkHttpResponse::ckBodyStr(resp)

    If respStatusCode <> 200
        CkHttpResponse::ckDispose(resp)

        Debug "Failed in some unknown way."
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        CkPrng::ckDispose(prng)
        CkJsonObject::ckDispose(jsonBody)
        CkHttp::ckDispose(http)
        ProcedureReturn
    EndIf

    ;  When the response status code = 200, we'll have either
    ;  success response like this:
    ;   {"status":"1","authtoken":"...","sek":"..."}
    ; 
    ;  or a failed response like this:
    ; 
    ;  {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}

    ;  Load the response body into a JSON object.
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckLoad(json,CkHttpResponse::ckBodyStr(resp))
    CkHttpResponse::ckDispose(resp)

    status.i = CkJsonObject::ckIntOf(json,"status")
    Debug "status = " + Str(status)

    If status <> 1
        ;  Failed.  Base64 decode the error
        ; {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}
        ;  For an invalid password, the error is: {"errorCodes":"108"}
        sbError.i = CkStringBuilder::ckCreate()
        If sbError.i = 0
            Debug "Failed to create object."
            ProcedureReturn
        EndIf

        CkJsonObject::ckStringOfSb(json,"error",sbError)
        CkStringBuilder::ckDecode(sbError,"base64","utf-8")
        Debug "error: " + CkStringBuilder::ckGetAsString(sbError)
        CkPublicKey::ckDispose(pubkey)
        CkRsa::ckDispose(rsa)
        CkPrng::ckDispose(prng)
        CkJsonObject::ckDispose(jsonBody)
        CkHttp::ckDispose(http)
        CkJsonObject::ckDispose(json)
        CkStringBuilder::ckDispose(sbError)
        ProcedureReturn
    EndIf

    ;  At this point, we know the request was entirely successful.
    authToken.s = CkJsonObject::ckStringOf(json,"authtoken")

    ;  Decrypt the sek key using our app_key.
    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkCrypt2::setCkCryptAlgorithm(crypt, "aes")
    CkCrypt2::setCkCipherMode(crypt, "ecb")
    CkCrypt2::setCkKeyLength(crypt, 256)
    CkCrypt2::ckSetEncodedKey(crypt,app_key,"us-ascii")
    CkCrypt2::setCkEncodingMode(crypt, "base64")

    bdSek.i = CkBinData::ckCreate()
    If bdSek.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkBinData::ckAppendEncoded(bdSek,CkJsonObject::ckStringOf(json,"sek"),"base64")
    CkCrypt2::ckDecryptBd(crypt,bdSek)

    ;  bdSek now contains the decrypted symmetric encryption key...
    ;  We'll use it to encrypt the JSON payloads we send.

    ;  Let's persist our authtoken and decrypted sek (symmetric encryption key).
    ;  To send EWAY requests (such as to create an e-way bill), we'll just load
    ;  and use these pre-obtained credentials.
    jsonEwayAuth.i = CkJsonObject::ckCreate()
    If jsonEwayAuth.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckUpdateString(jsonEwayAuth,"authToken",authToken)
    CkJsonObject::ckUpdateString(jsonEwayAuth,"decryptedSek",CkBinData::ckGetEncoded(bdSek,"base64"))
    CkJsonObject::setCkEmitCompact(jsonEwayAuth, 0)

    fac.i = CkFileAccess::ckCreate()
    If fac.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkFileAccess::ckWriteEntireTextFile(fac,"qa_data/tokens/ewayAuth.json",CkJsonObject::ckEmit(jsonEwayAuth),"utf-8",0)

    Debug "Saved:"
    Debug CkJsonObject::ckEmit(jsonEwayAuth)

    ;  Sample output:
    ;  {
    ;    "authToken": "IBTeFtxNfVurg71LTzZ2r0xK7",
    ;    "decryptedSek": "5g1TyTie7yoslU3DrbYATa7mWyPazlODE7cEh5Vy4Ho="
    ;  }


    CkPublicKey::ckDispose(pubkey)
    CkRsa::ckDispose(rsa)
    CkPrng::ckDispose(prng)
    CkJsonObject::ckDispose(jsonBody)
    CkHttp::ckDispose(http)
    CkJsonObject::ckDispose(json)
    CkStringBuilder::ckDispose(sbError)
    CkCrypt2::ckDispose(crypt)
    CkBinData::ckDispose(bdSek)
    CkJsonObject::ckDispose(jsonEwayAuth)
    CkFileAccess::ckDispose(fac)


    ProcedureReturn
EndProcedure