Compiler warns of the isServer function parameter being unused. Seems like it can, indeed, be safely removed:

--- tls.c       2020-10-12 16:39:22.000000000 -0400
+++ tls.c       2023-11-19 21:30:03.357601000 -0500
@@ -62,5 +62,5 @@
                        Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]);

-static SSL_CTX *CTX_Init(State *statePtr, int isServer, int proto, char *key,
+static SSL_CTX *CTX_Init(State *statePtr, int proto, char *key,
                        char *certfile, unsigned char *key_asn1, unsigned char *cert_asn1,
                        int key_asn1_len, int cert_asn1_len, char *CAdir, char *CAfile,
@@ -897,5 +897,5 @@
        ctx = ((State *)Tcl_GetChannelInstanceData(chan))->ctx;
     } else {
-       if ((ctx = CTX_Init(statePtr, server, proto, keyfile, certfile, key,
+       if ((ctx = CTX_Init(statePtr, proto, keyfile, certfile, key,
     cert, key_len, cert_len, CAdir, CAfile, ciphers,
     DHparams)) == (SSL_CTX*)0) {
@@ -1067,8 +1067,7 @@

 static SSL_CTX *
-CTX_Init(statePtr, isServer, proto, keyfile, certfile, key, cert,
+CTX_Init(statePtr, proto, keyfile, certfile, key, cert,
          key_len, cert_len, CAdir, CAfile, ciphers, DHparams)
     State *statePtr;
-    int isServer;
     int proto;
     char *keyfile;