tls13-docs: mention it is only for OpenSSL >= 1.1.1

Reported-by: Jay Satiro
Co-authored-by: Jay Satiro
Fixes #3938
Closes #3946

docs/CIPHERS.md

@@ -6,11 +6,12 @@ and
 [`--ciphers`](https://curl.haxx.se/docs/manpage.html#--ciphers)
 users can control which ciphers to consider when negotiating TLS connections.
 
-TLS 1.3 ciphers are supported since curl 7.61 with options
+TLS 1.3 ciphers are supported since curl 7.61 for OpenSSL 1.1.1+ with options
 [`CURLOPT_TLS13_CIPHERS`](https://curl.haxx.se/libcurl/c/CURLOPT_TLS13_CIPHERS.html)
 and
 [`--tls13-ciphers`](https://curl.haxx.se/docs/manpage.html#--tls13-ciphers)
-.
+. If you are using a different SSL backend you can try setting TLS 1.3 cipher
+suites by using the respective regular cipher option.
 
 The names of the known ciphers differ depending on which TLS backend that
 libcurl was built to use. This is an attempt to list known cipher names.

docs/cmdline-opts/proxy-tls13-ciphers.d

@@ -9,4 +9,8 @@ ciphers. Read up on TLS 1.3 cipher suite details on this URL:
 
  https://curl.haxx.se/docs/ssl-ciphers.html
 
+This option is currently used only when curl is built to use OpenSSL 1.1.1 or
+later. If you are using a different SSL backend you can try setting TLS 1.3
+cipher suites by using the --proxy-ciphers option.
+
 If this option is used several times, the last one will be used.

docs/cmdline-opts/tls13-ciphers.d

@@ -9,4 +9,8 @@ cipher suite details on this URL:
 
  https://curl.haxx.se/docs/ssl-ciphers.html
 
+This option is currently used only when curl is built to use OpenSSL 1.1.1 or
+later. If you are using a different SSL backend you can try setting TLS 1.3
+cipher suites by using the --ciphers option.
+
 If this option is used several times, the last one will be used.

docs/libcurl/opts/CURLOPT_PROXY_TLS13_CIPHERS.3

@@ -37,6 +37,10 @@ You'll find more details about cipher lists on this URL:
 
  https://curl.haxx.se/docs/ssl-ciphers.html
 
+This option is currently used only when curl is built to use OpenSSL 1.1.1 or
+later. If you are using a different SSL backend you can try setting TLS 1.3
+cipher suites by using the CURLOPT_PROXY_SSL_CIPHER_LIST option.
+
 The application does not have to keep the string around after setting this
 option.
 .SH DEFAULT

docs/libcurl/opts/CURLOPT_TLS13_CIPHERS.3

@@ -36,6 +36,10 @@ You'll find more details about cipher lists on this URL:
 
  https://curl.haxx.se/docs/ssl-ciphers.html
 
+This option is currently used only when curl is built to use OpenSSL 1.1.1 or
+later. If you are using a different SSL backend you can try setting TLS 1.3
+cipher suites by using the CURLOPT_SSL_CIPHER_LIST option.
+
 The application does not have to keep the string around after setting this
 option.
 .SH DEFAULT

src/tool_help.c

@@ -335,8 +335,8 @@ static const struct helptxt helptext[] = {
    "SPNEGO proxy service name"},
   {"    --proxy-ssl-allow-beast",
    "Allow security flaw for interop for HTTPS proxy"},
-  {"    --proxy-tls13-ciphers <ciphersuite list>",
+  {"    --proxy-tls13-ciphers <list>",
-   "TLS 1.3 proxy cipher suites"},
+   "TLS 1.3 ciphersuites for proxy (OpenSSL)"},
   {"    --proxy-tlsauthtype <type>",
    "TLS authentication type for HTTPS proxy"},
   {"    --proxy-tlspassword <string>",
@@ -445,8 +445,8 @@ static const struct helptxt helptext[] = {
    "Transfer based on a time condition"},
   {"    --tls-max <VERSION>",
    "Set maximum allowed TLS version"},
-  {"    --tls13-ciphers <list of TLS 1.3 ciphersuites>",
+  {"    --tls13-ciphers <list>",
-   "TLS 1.3 cipher suites to use"},
+   "TLS 1.3 ciphersuites (OpenSSL)"},
   {"    --tlsauthtype <type>",
    "TLS authentication type"},
   {"    --tlspassword",