cmake: warn for OpenSSL versions missing TLS 1.3 support

To match existing warnings for Secure Transport and BearSSL.

OpenSSL 1.1.1 or upper are offering TLS 1.3 support.

Ref: https://wiki.openssl.org/index.php/TLS1.3

Closes #16120

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2d869882fe2b9f3da17d0b8626213ca2b91f2258..0a81ef41e14db4f291a2ba14befe721f453e1879 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -778,6 +778,9 @@ if(CURL_USE_OPENSSL)
     set(_openssl "AmiSSL")
   else()
     set(_openssl "OpenSSL")
+    if(OPENSSL_VERSION VERSION_LESS 1.1.1)
+      message(WARNING "OpenSSL ${OPENSSL_VERSION} does not support TLS 1.3.")
+    endif()
   endif()
 endif()