NXPY-201: Allow more extensability of request_token()

[BoboTiG]

Also simplified the OAuth2Error exception as the stacktrace was not useful.

[nuxeojenkins]

View issue in JIRA: NXPY-201: Implement support for OAuth2

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.23%.

Quality metrics	Before	After	Change
Complexity	1.12 ⭐	1.12 ⭐	0.00
Method Length	21.36 ⭐	21.18 ⭐	-0.18 👍
Working memory	5.26 ⭐	5.19 ⭐	-0.07 👍
Quality	89.46% ⭐	89.69% ⭐	0.23% 👍

Other metrics	Before	After	Change
Lines	317	321	4

Changed files	Quality Before	Quality After	Quality Change
nuxeo/exceptions.py	92.49% ⭐	92.60% ⭐	0.11% 👍
nuxeo/auth/oauth2.py	80.52% ⭐	80.76% ⭐	0.24% 👍
tests/test_exception.py	95.55% ⭐	95.98% ⭐	0.43% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
nuxeo/auth/oauth2.py	OAuth2.create_authorization_url	0 ⭐	39 ⭐	10 😞	78.27% ⭐	Extract out complex expressions

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[codecov]

Codecov Report

Merging #233 (b45ba7b) into master (afec724) will not change coverage.
The diff coverage is 71.42%.

@@           Coverage Diff           @@
##           master     #233   +/-   ##
=======================================
  Coverage   96.80%   96.80%           
=======================================
  Files          29       29           
  Lines        1782     1782           
=======================================
  Hits         1725     1725           
  Misses         57       57           

Flag	Coverage Δ
unit	96.80% <71.42%> (ø)

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Impacted Files	Coverage Δ
nuxeo/auth/oauth2.py	76.92% <50.00%> (ø)
nuxeo/exceptions.py	100.00% <100.00%> (ø)

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