make all header names case insensitive

[RoboSparrow]

https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2

Field names are case-insensitive.

A good example is the new Javascript fetch api who lowercases all header names by default

Fetch is now supported by all browsers

const headers = {
    'Authorization': 'Basic ' + btoa(lrs.auth),
    'X-Experience-API-Version':  lrs.version,
    'Content-Type': 'application/json',
};

fetch(url, {
    method: 'GET',
    headers: new Headers(headers),
    mode: 'cors'
}).then((res) => {
    //success
}).catch((error) => {
    //error
})
;

Request headers

Accept:*/*
Accept-Encoding:gzip, deflate, br
Accept-Language:en-US,en;q=0.8,de;q=0.6
authorization:Basic MHBSRzViaU9UZ1E3NjJkaUZvbmRJdzVCS0poRGtLbEwzdUl5Z1VCOTprSEMxekJ3b2t4a0YxakhWRGdDckplWXM1M2lMR1ZqMFNBRnRMRHZV
Cache-Control:no-cache
Connection:keep-alive
content-type:application/json
Host:sandbox.experience.at
Origin:http://localhost:3000
Pragma:no-cache
Referer:http://localhost:3000/
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.109 Safari/537.36
x-experience-api-version:1.0.2

Response

401 Unauthorized {"error_message":"Credentials invalid!"}

[RoboSparrow]

I think this issue exists where we work with Slim's $request->rawHeaders()

[RoboSparrow]

@sraka1 see PR comments

[RoboSparrow]

end-to-end tests (npm update required!): https://github.com/Brightcookie/lx-Test-Suite/commit/105073d9c65c711b168d191100b8f2014bc4693b

node test -d test/fetchApi