Handle user create race condition

[jvlcek]

Fixes #20041

When a user's credentials are used to access ManageIQ for the first time, if properly configured, the user record will be created in the ManageIQ database.

It is possible when multiple simultaneous attempts to access ManageIQ for the first time with a single user name that a race condition could result in multiple user records being created for the same user.

This PR addresses this race condition by placing a lock on the User table when attempting
to create a new user. If a duplicate user record is found at this time it means a different simultaneous login attempt has been completed before the current one. To avoid raising a duplicate userid error this condition is rescued and handled by attempting to update, the existing user record instead of creating a new on.

Steps for Testing/QA [Optional]

Configure ManageIQ for external auth, with get user groups from Identity Provider selected.
Perform multiple simultaneous attempts to access the ManageIQ API with a username and password for a user that is not yet in the database.

This can be done with a shell script that issues multiple simultaneous curl commands to query ManageIQ.

e.g.: Repeat the below line multiple times in a shell script and run the shell script simultaneously from multiple shell windows

curl --user test_user:<PW> -k -X GET -H "Accept: application/json" https:/my_miq.example.com:443/api &

[jvlcek]

@miq-bot add_label bug
@miq-bot add_label authentication
@miq-bot assign @abellotti

[miq-bot]

@jvlcek Cannot apply the following label because they are not recognized:

• authentication

All labels for ManageIQ/manageiq: https://github.com/ManageIQ/manageiq/labels

[jvlcek]

@bdunne Please review

[kbrock]

This looks great. good way to setup the testing.

[miq-bot]

Checked commit jvlcek@49e37d0 with ruby 2.5.7, rubocop 0.69.0, haml-lint 0.28.0, and yamllint
2 files checked, 0 offenses detected
Everything looks fine. ⭐

[Fryguy]

I like that we only lock on a new user, which should ideally be less common than just logging in. This is great!

[Fryguy]

@jvlcek @abellotti I think this bug has been around a while...should this be backported to ivanchuk as well?

[jvlcek]

@Fryguy Thank you for merging. Yes it probably should go to ivanchuck as well.

[jvlcek]

@miq-bot add_label Ivanchuk/yes

[simaishi]

Jansa backport details:

$ git log -1
commit 31cbbcf94e8b0c974202494f7e93f8925ef07874
Author: Jason Frey <fryguy9@gmail.com>
Date:   Fri Apr 24 13:37:41 2020 -0400

    Merge pull request #20097 from jvlcek/multi_user_race_ISSUE_20041

    Handle user create race condition

    (cherry picked from commit 5906889e13d8670376e9f7624457dac8abf7ba0b)