title: PHP with openSSL - supplied key param cannot be coerced into a private key
body: <p>I'm trying to sign a file using <code>openssl_sign()</code> function. I have the following private key:
  <code>
  -----BEGIN EC PRIVATE KEY-----
  MHQCAQEEIDzQVg9bJ1kZFsZDoLeqadA4OTgKc40ukSmQ3MVzcV0soAcGBSuBBAAK
  oUQDQgAEvzUNKCE3UVimCLUePomOUH/kfy0ujHdN5Kmn7ez3TtokJDy5ksVnOgf6
  WzpmzY46zvKAnQ44Cgx5Kdqx5dVDiw==
  -----END EC PRIVATE KEY-----
  </code></p>
  
  <p>I'm using the following function: <code>openssl_sign("test", $signature, $private_key, OPENSSL_ALGO_SHA256);</code>.</p>
  
  <p>I have one server that is able to sign using the given key and one that is not. The one that is has PHP 5.6 and the one that is not has PHP 7.1 . How come one server is able to use the key and one is not?</p>