Allow Ecdsa keys as oauth2 server

[shyim]

Currently, the algo is hard-coded here https://github.com/thephpleague/oauth2-server/blob/master/src/Entities/Traits/AccessTokenTrait.php#L47

Switching it does not work in any case, but you get at least a key. Verifiying seems also hard-coded somewhere

[Sephster]

Thank you. This implementation is hopefully just a stop gap until we drop PHP 7 support all together. I will flag this for addressing in the next major.

[mostafa-rz]

I think the verifying also takes place in this method:

oauth2-server/src/AuthorizationValidators/BearerTokenValidator.php

Line 69 in 0f32fbe

private function initJwtConfiguration()