[AIRFLOW-4934] Fix ProxyFix due to Werkzeug upgrade

[nritholtz]

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https://issues.apache.org/jira/browse/AIRFLOW-4934

Description

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Since Werkzeug 0.15, enable_proxy_fix doesn't work as expected as per this Github issue.

We should fix it to at least respect what was previous behavior. We can eventually also offer a configuration to customize the new behavior, however this is breaking old behavior, and is (I believe) required within the next/current Airflow release due to Flask pinning the Werkzeug version.

Tests

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Consumption of Werkzeug client (similar to #3983)

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• Passes flake8

[codecov-io]

Codecov Report

Merging #5563 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #5563      +/-   ##
=========================================
+ Coverage   78.99%     79%   +<.01%     
=========================================
  Files         489     489              
  Lines       30741   30741              
=========================================
+ Hits        24284   24287       +3     
+ Misses       6457    6454       -3

Impacted Files	Coverage Δ
airflow/www/app.py	97.32% <0%> (ø)	⬆️
airflow/models/taskinstance.py	93.18% <0%> (+0.49%)	⬆️

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[ashb]

Oh one thing: how does this work if Werkzeug 0.14 is still installed? Does that version accept the these arguments? if not we should pin Flask >=1.1.0

[ashb]

It does not, so this will break if anyone still has Werkzeug 0.14 installed. I'm going to revert this for now.

0.15 also moved the import to werkzeug.middleware.proxy_fix.ProxyFix.