Unable to get eventsources list using REST API

I am trying this and found several problems.

When using on the header, the "Content-Type" spec, I always get an error 500 with an "Unknown error" message. I tried removing it and it looks to work better.

Now I am getting a clear "Authentication failed" error message. I think the problem I have now is creating the correct authentication string. As this string is build with, among others, the request details, I don't know how to correctly append this "files" variable (a dictionary object) to the request variable using this piece of code:

#Concatenate Request details
requestVars = httpVerb + epoch + data + resourcePath

#Construct signature
signature = base64.b64encode(hmac.new(AccessKey,msg=requestVars,digestmod=hashlib.sha256).hexdigest())

#Construct headers
auth = 'LMv1 ' + AccessId + ':' + signature + ':' + epoch
headers = {'Authorization':auth}

In this case, "data" is not a string, but a dictionary containing a file object.

How authorization string should be built for this particular case?

I will have a look at the SDK anytime, as suggested.