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

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

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#import <CkoPublicKey.h>
#import <NSString.h>
#import <CkoRsa.h>
#import <CkoPrng.h>
#import <CkoJsonObject.h>
#import <CkoHttp.h>
#import <CkoHttpResponse.h>
#import <CkoStringBuilder.h>
#import <CkoCrypt2.h>
#import <CkoBinData.h>
#import <CkoFileAccess.h>

// 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
CkoPublicKey *pubkey = [[CkoPublicKey alloc] init];
BOOL success = [pubkey LoadFromFile: @"qa_data/pem/eway_publickey.pem"];
if (success != YES) {
    NSLog(@"%@",pubkey.LastErrorText);
    return;
}

// Encrypt the password using the RSA public key provided by eway..
NSString *password = @"my_wepgst_password";
CkoRsa *rsa = [[CkoRsa alloc] init];
rsa.Charset = @"utf-8";
rsa.EncodingMode = @"base64";

success = [rsa ImportPublicKeyObj: pubkey];
if (success != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Returns the encrypted password as base64 (because the EncodingMode = "base64")
NSString *encPassword = [rsa EncryptStringENC: password bUsePrivateKey: NO];
if (rsa.LastMethodSuccess != YES) {
    NSLog(@"%@",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.
CkoPrng *prng = [[CkoPrng alloc] init];
// Generate a random string containing some numbers, uppercase, and lowercase.
NSString *app_key = [prng RandomString: [NSNumber numberWithInt: 32] bDigits: YES bLower: YES bUpper: YES];

NSLog(@"%@%@",@"app_key = ",app_key);

// RSA encrypt the app_key.
NSString *encAppKey = [rsa EncryptStringENC: app_key bUsePrivateKey: NO];
if (rsa.LastMethodSuccess != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

// Prepare the JSON body for the HTTP POST that gets the access token.
CkoJsonObject *jsonBody = [[CkoJsonObject alloc] init];
[jsonBody UpdateString: @"action" value: @"ACCESSTOKEN"];
// Use your username instead of "09ABDC24212B1FK".
[jsonBody UpdateString: @"username" value: @"09ABDC24212B1FK"];
[jsonBody UpdateString: @"password" value: encPassword];
[jsonBody UpdateString: @"app_key" value: encAppKey];

CkoHttp *http = [[CkoHttp alloc] init];

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

// POST the JSON...
CkoHttpResponse *resp = [http PostJson2: @"http://ewb.wepgst.com/api/Authenticate" contentType: @"application/json" jsonText: [jsonBody Emit]];
if (http.LastMethodSuccess != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

int respStatusCode = [resp.StatusCode intValue];
NSLog(@"%@%d",@"response status code =",respStatusCode);
NSLog(@"%@",@"response body:");
NSLog(@"%@",resp.BodyStr);

if (respStatusCode != 200) {

    NSLog(@"%@",@"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.
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json Load: resp.BodyStr];

int status = [[json IntOf: @"status"] intValue];
NSLog(@"%@%d",@"status = ",status);

if (status != 1) {
    // Failed.  Base64 decode the error
    // {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}
    // For an invalid password, the error is: {"errorCodes":"108"}
    CkoStringBuilder *sbError = [[CkoStringBuilder alloc] init];
    [json StringOfSb: @"error" sb: sbError];
    [sbError Decode: @"base64" charset: @"utf-8"];
    NSLog(@"%@%@",@"error: ",[sbError GetAsString]);
    return;
}

// At this point, we know the request was entirely successful.
NSString *authToken = [json StringOf: @"authtoken"];

// Decrypt the sek key using our app_key.
CkoCrypt2 *crypt = [[CkoCrypt2 alloc] init];
crypt.CryptAlgorithm = @"aes";
crypt.CipherMode = @"ecb";
crypt.KeyLength = [NSNumber numberWithInt:256];
[crypt SetEncodedKey: app_key encoding: @"us-ascii"];
crypt.EncodingMode = @"base64";

CkoBinData *bdSek = [[CkoBinData alloc] init];
[bdSek AppendEncoded: [json StringOf: @"sek"] encoding: @"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.
CkoJsonObject *jsonEwayAuth = [[CkoJsonObject alloc] init];
[jsonEwayAuth UpdateString: @"authToken" value: authToken];
[jsonEwayAuth UpdateString: @"decryptedSek" value: [bdSek GetEncoded: @"base64"]];
jsonEwayAuth.EmitCompact = NO;

CkoFileAccess *fac = [[CkoFileAccess alloc] init];
[fac WriteEntireTextFile: @"qa_data/tokens/ewayAuth.json" fileData: [jsonEwayAuth Emit] charset: @"utf-8" includePreamble: NO];

NSLog(@"%@",@"Saved:");
NSLog(@"%@",[jsonEwayAuth Emit]);

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