From OpenID Connect Client Registration Spec: ["Implementations MUST support TLS."](https://openid.net/specs/openid-connect-registration-1_0.html#TLSRequirements)
Also, ["Communication with the Authorization Endpoint MUST utilize TLS."](https://openid.net/specs/openid-connect-core-1_0.html#AuthorizationEndpoint)
Basically, the whole trust model for OpenID Connect requires TLS. Without TLS, more signing and encryption would be required (like in OAuth 1.0).
Also, `localhost` should only be used for browser based native applications.
Please review the OpenID Connect specs.