3.2.3.2 Transport Layer Security
Connection over Transport Layer Security (TLS) functions as specified in [RFC7540] section 3.3, with the modifications described in this section.
Servers SHOULD select TLS 1.2 ([RFC5246]) or greater for all connections, and MAY<4> generate a connection error of type INADEQUATE_SECURITY (see [RFC7540] section 9.2) if the client’s highest offered TLS version is less than 1.2.
Servers MUST select a cipher suite over which they are willing to use HTTP/2. They MUST NOT generate a connection error of type INADEQUATE_SECURITY after selecting TLS version 1.2 or higher and a cipher suite included in the client’s ClientHello message, regardless of whether the selected cipher suite is included in [RFC7540] Appendix A.
Servers SHOULD set the TLS_RENEG_PERMITTED setting to a non-zero value if their TLS library and the negotiated TLS version support renegotiation, and the server is willing<5> to employ it.