Implement Saml integration

[javierdelapuente]

Applicable spec: ISD140

Overview

This PR adds Saml support to paas-app-charmer using the saml-integrator charm.

All the following env variables will be available to the paas-app-charmer workload if Saml is integrated correctly with a paas-app-charmer generated project:

SAML_SINGLE_SIGN_ON_REDIRECT_URL
SAML_METADATA_URL
SAML_ENTITY_ID
SAML_SIGNING_CERTIFICATE

These variables contain enough information about the IdP for the SP, so projects (or frameworks) based on libraries like python3-saml and pysaml2 could easily use Saml with those env variables.

An integration test that generates the env variables from the saml-integration has been written. However, no real Saml authentication has been done in this test, as that would introduce extra complexity to the test that will test a Saml library, not the injection of the env variables.

Rationale

Saml is a widely used standard for authentication/authorization, and paas-app-charmer apps can benefit from it.

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

[cbartz]

LGTM

[github-actions]

Test coverage for e0e5f0b

Name                                            Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------------------------------------
paas_app_charmer/__init__.py                       29     14      0      0    52%   13-14, 19-20, 26-27, 33-34, 40-41, 47-48, 54-55
paas_app_charmer/_gunicorn/__init__.py              0      0      0      0   100%
paas_app_charmer/_gunicorn/charm.py               164     25     26      4    84%   32-33, 40-41, 160-161, 163-164, 185->exit, 197-201, 215-217, 284-285, 290, 295, 300, 310, 315, 320, 325, 330, 345
paas_app_charmer/_gunicorn/charm_state.py         103      1     18      1    98%   175
paas_app_charmer/_gunicorn/charm_utils.py          23      0      0      0   100%
paas_app_charmer/_gunicorn/observability.py        13      0      2      0   100%
paas_app_charmer/_gunicorn/secret_storage.py       13      0      0      0   100%
paas_app_charmer/_gunicorn/webserver.py            75      4     14      1    94%   156, 168-174
paas_app_charmer/_gunicorn/workload_config.py      19      0      0      0   100%
paas_app_charmer/_gunicorn/wsgi_app.py             78      0     38      0   100%
paas_app_charmer/database_migration.py             33      0      2      0   100%
paas_app_charmer/databases.py                      25      2     11      1    92%   89-90
paas_app_charmer/django/__init__.py                 1      0      0      0   100%
paas_app_charmer/django/charm.py                   45      6      6      1    86%   73-77, 99, 114-115
paas_app_charmer/exceptions.py                      5      0      0      0   100%
paas_app_charmer/flask/__init__.py                  1      0      0      0   100%
paas_app_charmer/flask/charm.py                    37      0      2      0   100%
paas_app_charmer/secret_storage.py                 39      3     16      5    85%   50, 54->53, 55->57, 85, 104
paas_app_charmer/utils.py                          11      0     12      0   100%
-------------------------------------------------------------------------------------------
TOTAL                                             714     55    147     13    92%

Static code analysis report

Run started:2024-06-10 07:26:52.188597

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1572
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):