Content-Type header check is not case insensitive

[noresistence]

Steps to reproduce the issue

Manage to get the key content-type instead of Content-Type in $response->headers and send the token as application/json.

Expected result

The token should be identified as application/json in

oauth2/src/Client.php

Line 90 in 6a9f29d

if (strpos($response->headers['Content-Type'], 'application/json') !== false)

Actual result

The header will not be identified correctly as content-type indicator.

According to RFC 2616 - "Hypertext Transfer Protocol -- HTTP/1.1", Section 4.2, "Message Headers", Field names are case-insensitive.

System information (as much as possible)

Appears on a fresh joomla install from docker image with tag "joomla:3-php7.1", as well as tag "joomla:3-php7.2", and tag "3" as of 17th of march.

Additional comments

Fix it by ensuring the check to be case insensitive.

[zero-24]

Please see here @noresistence #11 when this fixes your issue please close here.

[zero-24]

and mark a successful test to the PR.

[noresistence]

Thank you very much, @zero-24 and @mbabker; your fix solves our problem.

The header fields are accessed in a second place, though: in refreshToken(). I submitted pull request #11 for this.