Improved Auth Spec & challenge endpoint

[Moumouls]

Need: #1275

SDK Login update for: https://github.com/parse-community/parse-server

Note: On OSX can test integration with 3.6, and tests fails in mongo 4.0 due to invalid field name "length"

If CI pass then we have detected a regression between mongo 3.6 and 4.0 for field name length on objects

• Challenge mehod

[ghost]

	Warnings
⚠️	Please add a changelog entry for your changes.

Generated by 🚫 dangerJS

[codecov]

Codecov Report

Merging #1276 (c787972) into master (4a75d97) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head c787972 differs from pull request most recent head a31beb6. Consider uploading reports for the commit a31beb6 to get more accurate results

@@           Coverage Diff           @@
##           master    #1276   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          60       60           
  Lines        5847     5869   +22     
  Branches     1311     1320    +9     
=======================================
+ Hits         5844     5866   +22     
  Misses          3        3           

Impacted Files	Coverage Δ
src/ParseUser.js	99.59% <100.00%> (+0.01%)	⬆️

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[Moumouls]

Issue reported for Mongo 4.X and field name length: #1277

[Moumouls]

@dplewis if you have an idea on the failing integration test, npm run integration is okay on my side, may be a Github CI cache issue ?

[dplewis]

@Moumouls Can you update from master?

[Moumouls]

@dplewis if you have some suggestion about the failing test ? 🙂

[dplewis]

Can you update from master again? The new release removes the flaky tests.

[Moumouls]

Done @dplewis

[dblythy]

@Moumouls how is this coming along? Would be good to have implemented for Parse Server 6