Modifications of headers returned by Client.prepare_*_request affects future calls #873
Description
Describe the bug
If I modify the headers dictionary returned by a Client.prepare_*_request method, the future calls to any of these methods return the modified headers.
How to reproduce
>>> import oauthlib.oauth2
>>> client = oauthlib.oauth2.WebApplicationClient('my client id')
>>> _, headers, _ = client.prepare_authorization_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded'}
>>> headers['Content-Length'] = '0'
>>> _, headers, _ = client.prepare_authorization_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded', 'Content-Length': '0'}
>>> _, headers, _ = client.prepare_token_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded', 'Content-Length': '0'}
>>> _, headers, _ = client.prepare_refresh_token_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded', 'Content-Length': '0'}Expected behavior
Either:
>>> import oauthlib.oauth2
>>> client = oauthlib.oauth2.WebApplicationClient('my client id')
>>> _, headers, _ = client.prepare_authorization_request('https://example.com')
>>> headers['Content-Length'] = '0'
>>> _, headers, _ = client.prepare_authorization_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded'}
>>> _, headers, _ = client.prepare_token_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded'}
>>> _, headers, _ = client.prepare_refresh_token_request('https://example.com')
>>> headers
{'Content-Type': 'application/x-www-form-urlencoded'}or
>>> import oauthlib.oauth2
>>> client = oauthlib.oauth2.WebApplicationClient('my client id')
>>> _, headers, _ = client.prepare_authorization_request('https://example.com')
>>> try:
... headers['Content-Length'] = '0'
... except Exception:
... print('an exception occurred')
...
an exception occurredor
this unusual feature being documented
Additional context
Please provide any further context here.
- Are you using OAuth1, OAuth2 or OIDC? OAuth2
- Are you writing client or server side code? client
- If client, what provider are you connecting to? a custom one
- Are you using a downstream library, such as
requests-oauthlib,django-oauth-toolkit, ...? no