Fix/csrf headers

[RadovanTomik]

Negotiator pull request:

Description:

Fixes the use of CSRF headers and adds a CI test for request creation.

Checklist:

Make sure you tick all the boxes bellow if they are true or do not apply:

• [x] I have performed a self review of my code
• [x] My code follows Google Java Code style
• [x] I have made my code as simple as possible
• [x] I have added unit tests and the code coverage has not decreased
• [x] I have updated the documentation in all relevant places

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.50%. Comparing base (e4acfd7) to head (9ebdb37).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #261 +/- ## ========================================= Coverage 78.50% 78.50% Complexity 894 894 ========================================= Files 122 122 Lines 2740 2740 Branches 155 155 ========================================= Hits 2151 2151 Misses 490 490 Partials 99 99 ``` | [Flag](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/261/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/BBMRI-ERIC/negotiator/pull/261/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC) | `78.50% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BBMRI-ERIC#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.