(C#) Get E-way Bill System Access Token

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

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//  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
Chilkat.PublicKey pubkey = new Chilkat.PublicKey();
bool success = pubkey.LoadFromFile("qa_data/pem/eway_publickey.pem");
if (success != true) {
    Debug.WriteLine(pubkey.LastErrorText);
    return;
}

//  Encrypt the password using the RSA public key provided by eway..
string password = "my_wepgst_password";
Chilkat.Rsa rsa = new Chilkat.Rsa();
rsa.Charset = "utf-8";
rsa.EncodingMode = "base64";

success = rsa.ImportPublicKeyObj(pubkey);
if (success != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

//  Returns the encrypted password as base64 (because the EncodingMode = "base64")
string encPassword = rsa.EncryptStringENC(password,false);
if (rsa.LastMethodSuccess != true) {
    Debug.WriteLine(rsa.LastErrorText);
    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.
Chilkat.Prng prng = new Chilkat.Prng();
//  Generate a random string containing some numbers, uppercase, and lowercase.
string app_key = prng.RandomString(32,true,true,true);

Debug.WriteLine("app_key = " + app_key);

//  RSA encrypt the app_key.
string encAppKey = rsa.EncryptStringENC(app_key,false);
if (rsa.LastMethodSuccess != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

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

Chilkat.Http http = new Chilkat.Http();

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

//  POST the JSON...
Chilkat.HttpResponse resp = http.PostJson2("http://ewb.wepgst.com/api/Authenticate","application/json",jsonBody.Emit());
if (http.LastMethodSuccess != true) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

int respStatusCode = resp.StatusCode;
Debug.WriteLine("response status code =" + Convert.ToString(respStatusCode));
Debug.WriteLine("response body:");
Debug.WriteLine(resp.BodyStr);

if (respStatusCode != 200) {

    Debug.WriteLine("Failed in some unknown way.");
    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.
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.Load(resp.BodyStr);

int status = json.IntOf("status");
Debug.WriteLine("status = " + Convert.ToString(status));

if (status != 1) {
    //  Failed.  Base64 decode the error
    // {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}
    //  For an invalid password, the error is: {"errorCodes":"108"}
    Chilkat.StringBuilder sbError = new Chilkat.StringBuilder();
    json.StringOfSb("error",sbError);
    sbError.Decode("base64","utf-8");
    Debug.WriteLine("error: " + sbError.GetAsString());
    return;
}

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

//  Decrypt the sek key using our app_key.
Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.CryptAlgorithm = "aes";
crypt.CipherMode = "ecb";
crypt.KeyLength = 256;
crypt.SetEncodedKey(app_key,"us-ascii");
crypt.EncodingMode = "base64";

Chilkat.BinData bdSek = new Chilkat.BinData();
bdSek.AppendEncoded(json.StringOf("sek"),"base64");
crypt.DecryptBd(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.
Chilkat.JsonObject jsonEwayAuth = new Chilkat.JsonObject();
jsonEwayAuth.UpdateString("authToken",authToken);
jsonEwayAuth.UpdateString("decryptedSek",bdSek.GetEncoded("base64"));
jsonEwayAuth.EmitCompact = false;

Chilkat.FileAccess fac = new Chilkat.FileAccess();
fac.WriteEntireTextFile("qa_data/tokens/ewayAuth.json",jsonEwayAuth.Emit(),"utf-8",false);

Debug.WriteLine("Saved:");
Debug.WriteLine(jsonEwayAuth.Emit());

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