Decoding and encoding JSON in Django - django

Question

I was following some django rest framework tutorials and found some obscure codes. This snippet is from the customised user model, the project from which uses jwt for authentication.
As I commented in the snippet, I can't notice the reason Why they first encodes data and decode it again. I thought this kind of pattern is not only specific to this tutorial, but quite a general pattern. Could anyone explain me please?
def _generate_jwt_token(self):
"""
Generates a JSON Web Token that stores this user's ID and
has an expiry date set to 60 days into the future.
"""
dt = datetime.now() + timedelta(days=60)
token = jwt.encode({ #first encode here
'id': self.pk,
'exp': int(dt.strftime('%s'))
}, settings.SECRET_KEY, algorithm='HS256')
return token.decode('utf-8') #returns decoded object

Answer 1

“Encoding” usually refers to converting data to its binary representation (bytes).
JWT (JSON Web Token) encoding uses a specific data structure and cryptographic signing to allow secure, authenticated exchanges.
The steps to encode data as JWT are as follows :
The payload is converted to json and encoded using base64.
A header, specifying the token type (eg. jwt) and the signature algorithm to use (eg. HS256), is encoded similarly.
A signature is derived from your private key and the two previous values.
Result is obtained by joining header, payload and signature with dots. The output is a binary string.
More informations here.
Decoding it using UTF-8 transforms this binary string into an Unicode string :
>>> encoded_bin = jwt.encode({'some': 'data'}, 'secret_sig', algorithm='HS256')
>>> type(encoded_bin)
<class 'bytes'>
>>> encoded_string = encoded_bin.decode('utf-8')
>>> type(encoded_string)
<class 'str'>
Notes:
It is not always possible to decode bytes to string. Base64-encoding your data allows you to store any bytes as a text representation, but the encoded form requires more space (+33%) than it's raw representation.
A binary string is prefixed by a b in your Python interpreter (eg. b"a binary string")