Example in Python 3.x

from random import randint
from datetime import datetime
from urllib.parse import quote_plus
import hashlib

token = "65476hgfdsdf56656baa8b566c28"
print("Token:\n {0}\n".format(token))

secret = "gsfgf65sdsa4a8"
print("Secret:\n {0}\n".format(secret))

request = "http://site.meridix.se/api/customer/listcustomers"
verb = "GET"
print("Request:\n {0}\n".format(request))

nonce = randint(100000, 999999).__str__()
print("Nonce:\n {0}\n".format(nonce))

timestamp = datetime.utcnow().strftime("%Y%m%d%H%M%S")
print("Timestamp:\n {0}\n".format(timestamp))

parameters = [
"auth_nonce=" + nonce,
"auth_timestamp=" + timestamp,
"auth_token=" + token
]

parameters.sort()
print("Parameters:\n {0}\n".format(parameters))

parametersConcated = "&".join(parameters)
print("ParametersConcated:\n {0}\n".format(parametersConcated))

parametersConcatedEncoded = quote_plus(parametersConcated)
print("ParametersConcatedEncoded:\n {0}\n".format(parametersConcatedEncoded))

requestEncoded = quote_plus(request)
print("RequestEncoded:\n {0}\n".format(requestEncoded))

# IMPORTANT - The GET&-prefix must be change to POST& etc. when using different HTTP Verbs than GET.
verbRequestQuery = verb.upper() + "&" + requestEncoded + "&" + parametersConcatedEncoded + "&" + secret;
print("VerbRequestQuery:\n {0}\n".format(verbRequestQuery))

signature = hashlib.md5(verbRequestQuery.encode()).hexdigest()
print("Signature:\n {0}\n".format(signature))

signedRequest = request + "?" + parametersConcated + "&auth_signature=" + signature;
print("SignedRequest:\n {0}\n".format(signedRequest))