(C) Get E-way Bill System Access Token

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

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#include <C_CkPublicKey.h>
#include <C_CkRsa.h>
#include <C_CkPrng.h>
#include <C_CkJsonObject.h>
#include <C_CkHttp.h>
#include <C_CkHttpResponse.h>
#include <C_CkStringBuilder.h>
#include <C_CkCrypt2.h>
#include <C_CkBinData.h>
#include <C_CkFileAccess.h>

void ChilkatSample(void)
    {
    HCkPublicKey pubkey;
    BOOL success;
    const char *password;
    HCkRsa rsa;
    const char *encPassword;
    HCkPrng prng;
    const char *app_key;
    const char *encAppKey;
    HCkJsonObject jsonBody;
    HCkHttp http;
    HCkHttpResponse resp;
    int respStatusCode;
    HCkJsonObject json;
    int status;
    HCkStringBuilder sbError;
    const char *authToken;
    HCkCrypt2 crypt;
    HCkBinData bdSek;
    HCkJsonObject jsonEwayAuth;
    HCkFileAccess fac;

    //  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 = CkPublicKey_Create();
    success = CkPublicKey_LoadFromFile(pubkey,"qa_data/pem/eway_publickey.pem");
    if (success != TRUE) {
        printf("%s\n",CkPublicKey_lastErrorText(pubkey));
        CkPublicKey_Dispose(pubkey);
        return;
    }

    //  Encrypt the password using the RSA public key provided by eway..
    password = "my_wepgst_password";
    rsa = CkRsa_Create();
    CkRsa_putCharset(rsa,"utf-8");
    CkRsa_putEncodingMode(rsa,"base64");

    success = CkRsa_ImportPublicKeyObj(rsa,pubkey);
    if (success != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        return;
    }

    //  Returns the encrypted password as base64 (because the EncodingMode = "base64")
    encPassword = CkRsa_encryptStringENC(rsa,password,FALSE);
    if (CkRsa_getLastMethodSuccess(rsa) != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        return;
    }

    //  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 = CkPrng_Create();
    //  Generate a random string containing some numbers, uppercase, and lowercase.
    app_key = CkPrng_randomString(prng,32,TRUE,TRUE,TRUE);

    printf("app_key = %s\n",app_key);

    //  RSA encrypt the app_key.
    encAppKey = CkRsa_encryptStringENC(rsa,app_key,FALSE);
    if (CkRsa_getLastMethodSuccess(rsa) != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        CkPrng_Dispose(prng);
        return;
    }

    //  Prepare the JSON body for the HTTP POST that gets the access token.
    jsonBody = CkJsonObject_Create();
    CkJsonObject_UpdateString(jsonBody,"action","ACCESSTOKEN");
    //  Use your username instead of "09ABDC24212B1FK".
    CkJsonObject_UpdateString(jsonBody,"username","09ABDC24212B1FK");
    CkJsonObject_UpdateString(jsonBody,"password",encPassword);
    CkJsonObject_UpdateString(jsonBody,"app_key",encAppKey);

    http = CkHttp_Create();

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

    //  POST the JSON...
    resp = CkHttp_PostJson2(http,"http://ewb.wepgst.com/api/Authenticate","application/json",CkJsonObject_emit(jsonBody));
    if (CkHttp_getLastMethodSuccess(http) != TRUE) {
        printf("%s\n",CkHttp_lastErrorText(http));
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        CkPrng_Dispose(prng);
        CkJsonObject_Dispose(jsonBody);
        CkHttp_Dispose(http);
        return;
    }

    respStatusCode = CkHttpResponse_getStatusCode(resp);
    printf("response status code =%d\n",respStatusCode);
    printf("response body:\n");
    printf("%s\n",CkHttpResponse_bodyStr(resp));

    if (respStatusCode != 200) {
        CkHttpResponse_Dispose(resp);
        printf("Failed in some unknown way.\n");
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        CkPrng_Dispose(prng);
        CkJsonObject_Dispose(jsonBody);
        CkHttp_Dispose(http);
        return;
    }

    //  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 = CkJsonObject_Create();
    CkJsonObject_Load(json,CkHttpResponse_bodyStr(resp));
    CkHttpResponse_Dispose(resp);

    status = CkJsonObject_IntOf(json,"status");
    printf("status = %d\n",status);

    if (status != 1) {
        //  Failed.  Base64 decode the error
        // {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}
        //  For an invalid password, the error is: {"errorCodes":"108"}
        sbError = CkStringBuilder_Create();
        CkJsonObject_StringOfSb(json,"error",sbError);
        CkStringBuilder_Decode(sbError,"base64","utf-8");
        printf("error: %s\n",CkStringBuilder_getAsString(sbError));
        CkPublicKey_Dispose(pubkey);
        CkRsa_Dispose(rsa);
        CkPrng_Dispose(prng);
        CkJsonObject_Dispose(jsonBody);
        CkHttp_Dispose(http);
        CkJsonObject_Dispose(json);
        CkStringBuilder_Dispose(sbError);
        return;
    }

    //  At this point, we know the request was entirely successful.
    authToken = CkJsonObject_stringOf(json,"authtoken");

    //  Decrypt the sek key using our app_key.
    crypt = CkCrypt2_Create();
    CkCrypt2_putCryptAlgorithm(crypt,"aes");
    CkCrypt2_putCipherMode(crypt,"ecb");
    CkCrypt2_putKeyLength(crypt,256);
    CkCrypt2_SetEncodedKey(crypt,app_key,"us-ascii");
    CkCrypt2_putEncodingMode(crypt,"base64");

    bdSek = CkBinData_Create();
    CkBinData_AppendEncoded(bdSek,CkJsonObject_stringOf(json,"sek"),"base64");
    CkCrypt2_DecryptBd(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 = CkJsonObject_Create();
    CkJsonObject_UpdateString(jsonEwayAuth,"authToken",authToken);
    CkJsonObject_UpdateString(jsonEwayAuth,"decryptedSek",CkBinData_getEncoded(bdSek,"base64"));
    CkJsonObject_putEmitCompact(jsonEwayAuth,FALSE);

    fac = CkFileAccess_Create();
    CkFileAccess_WriteEntireTextFile(fac,"qa_data/tokens/ewayAuth.json",CkJsonObject_emit(jsonEwayAuth),"utf-8",FALSE);

    printf("Saved:\n");
    printf("%s\n",CkJsonObject_emit(jsonEwayAuth));

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


    CkPublicKey_Dispose(pubkey);
    CkRsa_Dispose(rsa);
    CkPrng_Dispose(prng);
    CkJsonObject_Dispose(jsonBody);
    CkHttp_Dispose(http);
    CkJsonObject_Dispose(json);
    CkStringBuilder_Dispose(sbError);
    CkCrypt2_Dispose(crypt);
    CkBinData_Dispose(bdSek);
    CkJsonObject_Dispose(jsonEwayAuth);
    CkFileAccess_Dispose(fac);

    }