[AIRFLOW-XXX] Add a third way to configure authorization

[mik-laj]

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Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-XXX
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.
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Description

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Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

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  • All the public functions and the classes in the PR contain docstrings that explain what it does
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[codecov-io]

Codecov Report

Merging #6134 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6134      +/-   ##
==========================================
+ Coverage      80%   80.03%   +0.02%     
==========================================
  Files         607      607              
  Lines       35006    35085      +79     
==========================================
+ Hits        28007    28079      +72     
- Misses       6999     7006       +7

Impacted Files	Coverage Δ
airflow/contrib/hooks/grpc_hook.py	92.06% <0%> (-1.27%)	⬇️
airflow/operators/docker_operator.py	95.74% <0%> (-1%)	⬇️
airflow/models/taskinstance.py	93.22% <0%> (-0.51%)	⬇️
airflow/models/baseoperator.py	95.1% <0%> (-0.25%)	⬇️
airflow/kubernetes/pod.py	91.66% <0%> (ø)	⬆️
airflow/api/auth/backend/kerberos_auth.py	84% <0%> (ø)	⬆️
airflow/utils/strings.py	100% <0%> (ø)	⬆️
airflow/gcp/operators/mlengine.py	75.72% <0%> (ø)	⬆️
airflow/exceptions.py	100% <0%> (ø)	⬆️
airflow/gcp/hooks/mlengine.py	20.66% <0%> (ø)	⬆️
... and 28 more

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