Failing to test POST in Django - json

Question

Using Python3, Django, and Django Rest Frameworks.
Previously I had a test case that was making a POST to an endpoint.
The payload was a dictionary:
mock_data = {some data here}
In order to send the data over the POST I was doing:
mock_data = base64.b64encode(json.dumps(mock_data).encode('utf-8'))
When doing the POST:
response = self.client.post(
'/some/path/here/', {
...,
'params': mock_data.decode('utf-8'),
},
)
And on the receiving end, in validate() method I was doing:
params = data['params']
try:
params_str = base64.b64decode(params).decode('utf-8')
app_data = json.loads(params_str)
except (UnicodeDecodeError, ValueError):
app_data = None
That was all fine, but now I need to use some hmac validation, and the json I am passing can no longer be a dict - its ordering would change each time, so hmac.new(secret, payload, algorithm) would be different.
I was trying to use a string:
payload = """{data in json format}"""
But when I am doing:
str_payload = payload.encode('utf-8')
b64_payload = base64.b64encode(str_payload)
I cannot POST it, and getting an error:
raise TypeError(repr(o) + " is not JSON serializable")
TypeError: b'ewog...Cn0=' is not JSON serializable
even if I do b64_payload.decode('utf-8') like before, still getting similar error:
raise TypeError(repr(o) + " is not JSON serializable")
TypeError: b'\xa2\x19...\xff' is not JSON serializable
Some python in the terminal:
>>> d = {'email': 'user#mail.com'} # regular dictionary
>>> d
{'email': 'user#mail.com'}
>>> dn = base64.b64encode(json.dumps(d).encode('utf-8'))
>>> dn
b'eyJlbWFpbCI6ICJ1c2VyQG1haWwuY29tIn0='
>>> s = """{"email": "user#mail.com"}""" # string
>>> s
'{"email": "user#mail.com"}'
>>> sn = base64.b64encode(json.dumps(s).encode('utf-8'))
>>> sn
b'IntcImVtYWlsXCI6IFwidXNlckBtYWlsLmNvbVwifSI=' # different!
>>> sn = base64.b64encode(s.encode('utf-8'))
>>> sn
b'eyJlbWFpbCI6ICJ1c2VyQG1haWwuY29tIn0=' # same

Answer 1

The issue is resolved.
The problem was NOT with the payload, but with a parameter I was passing:
signature': b'<signature'>
Solved by passing the signature field like this:
'signature': signature_b64.decode('utf-8')
Thank you!