Description:
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The CGI RFC at https://tools.ietf.org/rfc/rfc3875.txt specifies that the Content-Type header value should be stored in CONTENT_TYPE, but the built-in web server stores it in $_SERVER['HTTP_CONTENT_TYPE'] and does not create a $_SERVER['CONTENT_TYPE'] key. (This probably affects CONTENT_LENGTH as well.)

Test script:
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// put this in an index file and un the PHP web server against it,
// then issue `curl -H "Content-Type: application/json" http://localhost:8000`
// and see that there is no CONTENT_TYPE key, only HTTP_CONTENT_TYPE.
var_dump($_SERVER)

Expected result:
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Expected to see a CONTENT_TYPE key.

Actual result:
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Saw only HTTP_CONTENT_TYPE key.