Ada binding: add support for the PSK server callbacks

Plus fix location of the certificate files in the examples.

Tested with both Ada examples:
```
obj/tls_server_main --psk
obj/tls_client_main 127.0.0.1 --psk
```

wrapper/Ada/tls_client.adb

@@ -168,9 +168,9 @@ package body Tls_Client with SPARK_Mode is
 
    Any_Inet_Addr : Inet_Addr_Type renames SPARK_Sockets.Any_Inet_Addr;
 
-   CERT_FILE : constant String := "../../../certs/client-cert.pem";
-   KEY_FILE  : constant String := "../../../certs/client-key.pem";
-   CA_FILE   : constant String := "../../../certs/ca-cert.pem";
+   CERT_FILE : constant String := "../../certs/client-cert.pem";
+   KEY_FILE  : constant String := "../../certs/client-key.pem";
+   CA_FILE   : constant String := "../../certs/ca-cert.pem";
 
    subtype Byte_Array is WolfSSL.Byte_Array;
 
@@ -223,11 +223,10 @@ package body Tls_Client with SPARK_Mode is
          return;
       end if;
 
-      DTLS := (SPARK_Terminal.Argument_Count = 2 and then
-                Argument (2) = "--dtls");
-
-      PSK := (SPARK_Terminal.Argument_Count = 2 and then
-                Argument (2) = "--psk");
+      if Argument_Count = 2 then
+         DTLS := (Argument (2) = "--dtls");
+         PSK  := (Argument (2) = "--psk");
+      end if;
 
       if DTLS then
          SPARK_Sockets.Create_Datagram_Socket (C);
@@ -348,7 +347,6 @@ package body Tls_Client with SPARK_Mode is
       end if;
 
       if PSK then
-
          --  Use PSK for authentication.
          WolfSSL.Set_PSK_Client_Callback
            (Ssl      => Ssl,

wrapper/Ada/tls_server.adb

@@ -24,6 +24,8 @@ with Ada.Characters.Handling;
 with Ada.Strings.Bounded;
 with Ada.Text_IO.Bounded_IO;
 
+with Interfaces.C.Strings;
+
 with SPARK_Terminal; pragma Elaborate_All (SPARK_Terminal);
 
 package body Tls_Server with SPARK_Mode is
@@ -35,6 +37,9 @@ package body Tls_Server with SPARK_Mode is
 
    Success : WolfSSL.Subprogram_Result renames WolfSSL.Success;
 
+   subtype chars_ptr is WolfSSL.chars_ptr;
+   subtype unsigned is WolfSSL.unsigned;
+
    procedure Put (Char : Character) is
    begin
       Ada.Text_IO.Put (Char);
@@ -87,14 +92,66 @@ package body Tls_Server with SPARK_Mode is
 
    Any_Inet_Addr : Inet_Addr_Type renames SPARK_Sockets.Any_Inet_Addr;
 
-   CERT_FILE : constant String := "../../../certs/server-cert.pem";
-   KEY_FILE  : constant String := "../../../certs/server-key.pem";
-   CA_FILE   : constant String := "../../../certs/client-cert.pem";
+   CERT_FILE : constant String := "../../certs/server-cert.pem";
+   KEY_FILE  : constant String := "../../certs/server-key.pem";
+   CA_FILE   : constant String := "../../certs/client-cert.pem";
 
    subtype Byte_Array is WolfSSL.Byte_Array;
 
    Reply : constant Byte_Array := "I hear ya fa shizzle!";
 
+
+   function PSK_Server_Callback
+     (Unused         : WolfSSL.WolfSSL_Type;
+      Identity       : chars_ptr;
+      Key            : chars_ptr;
+      Key_Max_Length : unsigned) return unsigned
+   with Convention => C;
+
+   function PSK_Server_Callback
+     (Unused         : WolfSSL.WolfSSL_Type;
+      Identity       : chars_ptr;
+      Key            : chars_ptr;
+      Key_Max_Length : unsigned) return unsigned
+   with
+     SPARK_Mode => Off
+   is
+      use type Interfaces.C.unsigned;
+
+      --  Identity is OpenSSL testing default for openssl s_client, keep same
+      Identity_String : constant String := "Client_identity";
+      --  Test key in hex is 0x1a2b3c4d, in decimal 439,041,101
+      Key_String : constant String :=
+        Character'Val   (26)
+        & Character'Val (43)
+        & Character'Val (60)
+        & Character'Val (77);
+      --  These values are aligned with test values in wolfssl/wolfssl/test.h
+      --  and wolfssl-examples/psk/server-psk.c for testing interoperability.
+
+   begin
+
+      if Interfaces.C.Strings.Value
+        (Item   => Identity,
+         Length => Identity_String'Length) /= Identity_String or else
+         Key_Max_Length < Key_String'Length
+      then
+         return 0;
+      end if;
+
+      put_line (Interfaces.C.Strings.Value
+        (Item   => Identity,
+         Length => Identity_String'Length) );
+
+      Interfaces.C.Strings.Update
+        (Item   => Key,
+         Offset => 0,
+         Str    => Key_String,
+         Check  => False);
+
+      return Key_String'Length;
+   end PSK_Server_Callback;
+
    procedure Run (Ssl : in out WolfSSL.WolfSSL_Type;
                   Ctx : in out WolfSSL.Context_Type;
                   L   : in out SPARK_Sockets.Optional_Socket;
@@ -105,7 +162,7 @@ package body Tls_Server with SPARK_Mode is
       Ch : Character;
 
       Result : WolfSSL.Subprogram_Result;
-      DTLS : Boolean;
+      DTLS, PSK : Boolean;
       Shall_Continue : Boolean := True;
 
       Input  : WolfSSL.Read_Result;
@@ -119,14 +176,18 @@ package body Tls_Server with SPARK_Mode is
       end if;
 
       if SPARK_Terminal.Argument_Count > 1
-         or (SPARK_Terminal.Argument_Count = 1
-         and then SPARK_Terminal.Argument (1) /= "--dtls")
+         or (SPARK_Terminal.Argument_Count = 1 and then
+             SPARK_Terminal.Argument (1) /= "--dtls" and then
+             SPARK_Terminal.Argument (1) /= "--psk")
       then
-         Put_Line ("usage: tls_server_main [--dtls]");
+         Put_Line ("usage: tls_server_main [--dtls | --psk]");
          return;
       end if;
 
-      DTLS := (SPARK_Terminal.Argument_Count = 1);
+      if SPARK_Terminal.Argument_Count = 1 then
+         DTLS := (SPARK_Terminal.Argument (1) = "--dtls");
+         PSK  := (SPARK_Terminal.Argument (1) = "--psk");
+      end if;
 
       if DTLS then
          SPARK_Sockets.Create_Datagram_Socket (Socket => L);
@@ -197,63 +258,73 @@ package body Tls_Server with SPARK_Mode is
          return;
       end if;
 
-      --  Require mutual authentication.
-      WolfSSL.Set_Verify
-         (Context => Ctx,
-          Mode    => WolfSSL.Verify_Peer or WolfSSL.Verify_Fail_If_No_Peer_Cert);
+      if not PSK then
+         --  Require mutual authentication.
+         WolfSSL.Set_Verify
+            (Context => Ctx,
+            Mode    => WolfSSL.Verify_Peer or WolfSSL.Verify_Fail_If_No_Peer_Cert);
 
-      --  Check verify is set correctly (GitHub #7461)
-      if WolfSSL.Get_Verify(Context => Ctx) /= (WolfSSL.Verify_Peer or WolfSSL.Verify_Fail_If_No_Peer_Cert) then
-          Put ("Error: Verify does not match requested");
-          New_Line;
-          return;
+         --  Check verify is set correctly (GitHub #7461)
+         if WolfSSL.Get_Verify(Context => Ctx) /= (WolfSSL.Verify_Peer or WolfSSL.Verify_Fail_If_No_Peer_Cert) then
+               Put ("Error: Verify does not match requested");
+               New_Line;
+               return;
+         end if;
+
+         --  Load server certificates into WOLFSSL_CTX.
+         Result := WolfSSL.Use_Certificate_File (Context => Ctx,
+                                                 File    => CERT_FILE,
+                                                 Format  => WolfSSL.Format_Pem);
+         if Result /= Success then
+            Put ("ERROR: failed to load ");
+            Put (CERT_FILE);
+            Put (", please check the file.");
+            New_Line;
+            SPARK_Sockets.Close_Socket (L);
+            WolfSSL.Free (Context => Ctx);
+            Set (Exit_Status_Failure);
+            return;
+         end if;
+
+         --  Load server key into WOLFSSL_CTX.
+         Result := WolfSSL.Use_Private_Key_File (Context => Ctx,
+                                                 File    => KEY_FILE,
+                                                 Format  => WolfSSL.Format_Pem);
+         if Result /= Success then
+            Put ("ERROR: failed to load ");
+            Put (KEY_FILE);
+            Put (", please check the file.");
+            New_Line;
+            SPARK_Sockets.Close_Socket (L);
+            WolfSSL.Free (Context => Ctx);
+            Set (Exit_Status_Failure);
+            return;
+         end if;
+
+         --  Load client certificate as "trusted" into WOLFSSL_CTX.
+         Result := WolfSSL.Load_Verify_Locations (Context => Ctx,
+                                                  File    => CA_FILE,
+                                                  Path    => "");
+
+         if Result /= Success then
+            Put ("ERROR: failed to load ");
+            Put (CA_FILE);
+            Put (", please check the file.");
+            New_Line;
+            SPARK_Sockets.Close_Socket (L);
+            WolfSSL.Free (Context => Ctx);
+            Set (Exit_Status_Failure);
+            return;
+         end if;
       end if;
 
-      --  Load server certificates into WOLFSSL_CTX.
-      Result := WolfSSL.Use_Certificate_File (Context => Ctx,
-                                              File    => CERT_FILE,
-                                              Format  => WolfSSL.Format_Pem);
-      if Result /= Success then
-         Put ("ERROR: failed to load ");
-         Put (CERT_FILE);
-         Put (", please check the file.");
-         New_Line;
-         SPARK_Sockets.Close_Socket (L);
-         WolfSSL.Free (Context => Ctx);
-         Set (Exit_Status_Failure);
-         return;
+      if PSK then
+         --  Use PSK for authentication.
+         WolfSSL.Set_Context_PSK_Server_Callback
+            (Context  => Ctx,
+             Callback => PSK_Server_Callback'Access);
       end if;
-
-      --  Load server key into WOLFSSL_CTX.
-      Result := WolfSSL.Use_Private_Key_File (Context => Ctx,
-                                              File    => KEY_FILE,
-                                              Format  => WolfSSL.Format_Pem);
-      if Result /= Success then
-         Put ("ERROR: failed to load ");
-         Put (KEY_FILE);
-         Put (", please check the file.");
-         New_Line;
-         SPARK_Sockets.Close_Socket (L);
-         WolfSSL.Free (Context => Ctx);
-         Set (Exit_Status_Failure);
-         return;
-      end if;
-
-      --  Load client certificate as "trusted" into WOLFSSL_CTX.
-      Result := WolfSSL.Load_Verify_Locations (Context => Ctx,
-                                               File    => CA_FILE,
-                                               Path    => "");
-      if Result /= Success then
-         Put ("ERROR: failed to load ");
-         Put (CA_FILE);
-         Put (", please check the file.");
-         New_Line;
-         SPARK_Sockets.Close_Socket (L);
-         WolfSSL.Free (Context => Ctx);
-         Set (Exit_Status_Failure);
-         return;
-      end if;
-
+               
       while Shall_Continue loop
          pragma Loop_Invariant (not C.Exists);
          pragma Loop_Invariant (not WolfSSL.Is_Valid (Ssl));

wrapper/Ada/wolfssl.adb

@@ -592,6 +592,36 @@ package body WolfSSL is
       WolfSSL_Set_Psk_Client_Callback (Ssl, Callback);
    end Set_PSK_Client_Callback;
 
+   procedure WolfSSL_Set_Psk_Server_Callback
+     (Ssl : WolfSSL_Type;
+      Cb  : PSK_Server_Callback)
+   with
+     Convention    => C,
+     External_Name => "wolfSSL_set_psk_server_callback",
+     Import        => True;
+
+   procedure Set_PSK_Server_Callback
+       (Ssl      : WolfSSL_Type;
+        Callback : PSK_Server_Callback) is
+   begin
+      WolfSSL_Set_Psk_Server_Callback (Ssl, Callback);
+   end Set_PSK_Server_Callback;
+
+   procedure WolfSSL_CTX_Set_Psk_Server_Callback
+     (Ctx : Context_Type;
+      Cb  : PSK_Server_Callback)
+   with
+     Convention    => C,
+     External_Name => "wolfSSL_CTX_set_psk_server_callback",
+     Import        => True;
+
+   procedure Set_Context_PSK_Server_Callback
+       (Context  : Context_Type;
+        Callback : PSK_Server_Callback) is
+   begin
+      WolfSSL_CTX_Set_Psk_Server_Callback (Context, Callback);
+   end Set_Context_PSK_Server_Callback;
+
    function WolfSSL_Set_Fd (Ssl : WolfSSL_Type; Fd : int) return int with
      Convention    => C,
      External_Name => "wolfSSL_set_fd",

wrapper/Ada/wolfssl.ads

@@ -328,6 +328,36 @@ package WolfSSL with SPARK_Mode is
      Pre => Is_Valid (Ssl);
      -- Sets the PSK client side callback.
 
+   
+   type PSK_Server_Callback is access function
+     (Ssl            : WolfSSL_Type;
+      Identity       : chars_ptr;
+      Key            : chars_ptr;
+      Key_Max_Length : unsigned)
+      return unsigned with
+     Convention => C;
+     --  Return value is the key length on success or zero on error.
+     --  PSK server callback parameters:
+     --  Ssl - Reference to the wolfSSL structure
+     --  Identity - The ID will be stored here. 
+     --  Key - The key will be stored here.
+     --  Key_Max_Length - The max size of the key.
+     --
+     --  The implementation of this callback will need `SPARK_Mode => Off`
+     --  since it will require the code to use the C memory model.
+
+   procedure Set_PSK_Server_Callback
+     (Ssl      : WolfSSL_Type;
+      Callback : PSK_Server_Callback) with
+     Pre => Is_Valid (Ssl);
+     -- Sets the PSK Server side callback.
+   
+   procedure Set_Context_PSK_Server_Callback
+     (Context  : Context_Type;
+      Callback : PSK_Server_Callback) with
+     Pre => Is_Valid (Context);
+     --  Sets the PSK callback for the server side in the WolfSSL Context. 
+   
    function Attach (Ssl    : WolfSSL_Type;
                     Socket : Integer)
                     return Subprogram_Result with