title: PyJWT raises Signature verification failed
body: <p>I'm trying to verify JWT which issued by ThingsBoard.
  But verification was failed with <code>Signature verification failed</code></p>
  
  <p>My test code is at below.</p>
  
  <pre><code>def test_jwt_decoding():
      jwt_options = {
          'verify_signature': True,
          'verify_exp': True,
          'verify_nbf': False,
          'verify_iat': True,
          'verify_aud': False
      }
      token = 'eyJhbGciOiJIUzUxMiJ9.eyJzdWIiOiJhZG1pbkB0LW1vbmV0LmNvbSIsInNjb3BlcyI6WyJURU5BTlRfQURNSU4iXSwidXNlcklkIjoiODNiYmEzNDAtMDI3ZC0xMWU4LWI4ZmEtYWY1YjU0OTEyMDA0IiwiZmlyc3ROYW1lIjoi7ISx64Ko7IucIiwibGFzdE5hbWUiOiLqtIDrpqzsnpAiLCJlbmFibGVkIjp0cnVlLCJpc1B1YmxpYyI6ZmFsc2UsInRlbmFudElkIjoiMzkwMTNjNzAtMDI3ZC0xMWU4LWI4ZmEtYWY1YjU0OTEyMDA0IiwiY3VzdG9tZXJJZCI6IjEzODE0MDAwLTFkZDItMTFiMi04MDgwLTgwODA4MDgwODA4MCIsImlzcyI6InRoaW5nc2JvYXJkLmlvIiwiaWF0IjoxNTM1OTU1NDE2LCJleHAiOjM2NzU5NTU0MTZ9.N1Ms0LA7WtOel1pg6lTMRNDJosY3qfR6Q4SVuAUwmDPmTj4uYnKU0B-9Wdlqmg4HQRUXa23edOTU-TnAxfBoyg'
      try:
          jwt.decode(
              token,
              'thingsboardDefaultSigningKey',
              algorithms=['HS512'],
              options=jwt_options
          )
          assert True
      except Exception as err:
          print(str(err))
          assert False
  </code></pre>
  
  <p>I checked the signature was verified at jwt.io
  Only difference was <strong>secret base64 encoded</strong> on at jwt.io</p>
  
  <p><a href="https://i.stack.imgur.com/I1G4r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/I1G4r.png" alt="enter image description here"></a></p>
  
  <p>I'm gussing <strong>secret base64 encoded</strong> made this differences.<br>
  What should I do for that?</p>