(Tcl) Get E-way Bill System Access Token

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

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load ./chilkat.dll

# 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
set pubkey [new_CkPublicKey]

set success [CkPublicKey_LoadFromFile $pubkey "qa_data/pem/eway_publickey.pem"]
if {$success != 1} then {
    puts [CkPublicKey_lastErrorText $pubkey]
    delete_CkPublicKey $pubkey
    exit
}

# Encrypt the password using the RSA public key provided by eway..
set password "my_wepgst_password"
set rsa [new_CkRsa]

CkRsa_put_Charset $rsa "utf-8"
CkRsa_put_EncodingMode $rsa "base64"

set success [CkRsa_ImportPublicKeyObj $rsa $pubkey]
if {$success != 1} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    exit
}

# Returns the encrypted password as base64 (because the EncodingMode = "base64")
set encPassword [CkRsa_encryptStringENC $rsa $password 0]
if {[CkRsa_get_LastMethodSuccess $rsa] != 1} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    exit
}

# 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.
set prng [new_CkPrng]

# Generate a random string containing some numbers, uppercase, and lowercase.
set app_key [CkPrng_randomString $prng 32 1 1 1]

puts "app_key = $app_key"

# RSA encrypt the app_key.
set encAppKey [CkRsa_encryptStringENC $rsa $app_key 0]
if {[CkRsa_get_LastMethodSuccess $rsa] != 1} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    delete_CkPrng $prng
    exit
}

# Prepare the JSON body for the HTTP POST that gets the access token.
set jsonBody [new_CkJsonObject]

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

set http [new_CkHttp]

# 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_put_Accept $http "application/json"

# POST the JSON...
# resp is a CkHttpResponse
set resp [CkHttp_PostJson2 $http "http://ewb.wepgst.com/api/Authenticate" "application/json" [CkJsonObject_emit $jsonBody]]
if {[CkHttp_get_LastMethodSuccess $http] != 1} then {
    puts [CkHttp_lastErrorText $http]
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    delete_CkPrng $prng
    delete_CkJsonObject $jsonBody
    delete_CkHttp $http
    exit
}

set respStatusCode [CkHttpResponse_get_StatusCode $resp]
puts "response status code =$respStatusCode"
puts "response body:"
puts [CkHttpResponse_bodyStr $resp]

if {$respStatusCode != 200} then {
    delete_CkHttpResponse $resp

    puts "Failed in some unknown way."
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    delete_CkPrng $prng
    delete_CkJsonObject $jsonBody
    delete_CkHttp $http
    exit
}

# 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.
set json [new_CkJsonObject]

CkJsonObject_Load $json [CkHttpResponse_bodyStr $resp]
delete_CkHttpResponse $resp

set status [CkJsonObject_IntOf $json "status"]
puts "status = $status"

if {$status != 1} then {
    # Failed.  Base64 decode the error
    # {"status":"0","error":"eyJlcnJvckNvZGVzIjoiMTA4In0="}
    # For an invalid password, the error is: {"errorCodes":"108"}
    set sbError [new_CkStringBuilder]

    CkJsonObject_StringOfSb $json "error" $sbError
    CkStringBuilder_Decode $sbError "base64" "utf-8"
    puts "error: [CkStringBuilder_getAsString $sbError]"
    delete_CkPublicKey $pubkey
    delete_CkRsa $rsa
    delete_CkPrng $prng
    delete_CkJsonObject $jsonBody
    delete_CkHttp $http
    delete_CkJsonObject $json
    delete_CkStringBuilder $sbError
    exit
}

# At this point, we know the request was entirely successful.
set authToken [CkJsonObject_stringOf $json "authtoken"]

# Decrypt the sek key using our app_key.
set crypt [new_CkCrypt2]

CkCrypt2_put_CryptAlgorithm $crypt "aes"
CkCrypt2_put_CipherMode $crypt "ecb"
CkCrypt2_put_KeyLength $crypt 256
CkCrypt2_SetEncodedKey $crypt $app_key "us-ascii"
CkCrypt2_put_EncodingMode $crypt "base64"

set bdSek [new_CkBinData]

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.
set jsonEwayAuth [new_CkJsonObject]

CkJsonObject_UpdateString $jsonEwayAuth "authToken" $authToken
CkJsonObject_UpdateString $jsonEwayAuth "decryptedSek" [CkBinData_getEncoded $bdSek "base64"]
CkJsonObject_put_EmitCompact $jsonEwayAuth 0

set fac [new_CkFileAccess]

CkFileAccess_WriteEntireTextFile $fac "qa_data/tokens/ewayAuth.json" [CkJsonObject_emit $jsonEwayAuth] "utf-8" 0

puts "Saved:"
puts [CkJsonObject_emit $jsonEwayAuth]

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

delete_CkPublicKey $pubkey
delete_CkRsa $rsa
delete_CkPrng $prng
delete_CkJsonObject $jsonBody
delete_CkHttp $http
delete_CkJsonObject $json
delete_CkStringBuilder $sbError
delete_CkCrypt2 $crypt
delete_CkBinData $bdSek
delete_CkJsonObject $jsonEwayAuth
delete_CkFileAccess $fac