cmake: add support for building with wolfSSL

My working build cmdline:

$ cmake -DCMAKE_PREFIX_PATH=$HOME/build-wolfssl -DCMAKE_USE_WOLFSSL=ON .

Assisted-by: Brad King
Closes #5095

CMake/FindWolfSSL.cmake

@@ -0,0 +1,13 @@
+find_path(WolfSSL_INCLUDE_DIR NAMES wolfssl/ssl.h)
+find_library(WolfSSL_LIBRARY NAMES wolfssl)
+mark_as_advanced(WolfSSL_INCLUDE_DIR WolfSSL_LIBRARY)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(WolfSSL
+  REQUIRED_VARS WolfSSL_INCLUDE_DIR WolfSSL_LIBRARY
+  )
+
+if(WolfSSL_FOUND)
+  set(WolfSSL_INCLUDE_DIRS ${WolfSSL_INCLUDE_DIR})
+  set(WolfSSL_LIBRARIES ${WolfSSL_LIBRARY})
+endif()

CMakeLists.txt

@@ -298,7 +298,7 @@ if(WIN32)
 endif()
 
 # check SSL libraries
-# TODO support GnuTLS and WolfSSL
+# TODO support GnuTLS
 
 if(APPLE)
   option(CMAKE_USE_SECTRANSP "enable Apple OS native SSL/TLS" OFF)
@@ -311,9 +311,10 @@ endif()
 option(CMAKE_USE_MBEDTLS "Enable mbedTLS for SSL/TLS" OFF)
 option(CMAKE_USE_BEARSSL "Enable BearSSL for SSL/TLS" OFF)
 option(CMAKE_USE_NSS "Enable NSS for SSL/TLS" OFF)
+option(CMAKE_USE_WOLFSSL "enable wolfSSL for SSL/TLS" OFF)
 
 set(openssl_default ON)
-if(WIN32 OR CMAKE_USE_SECTRANSP OR CMAKE_USE_WINSSL OR CMAKE_USE_MBEDTLS OR CMAKE_USE_NSS)
+if(WIN32 OR CMAKE_USE_SECTRANSP OR CMAKE_USE_WINSSL OR CMAKE_USE_MBEDTLS OR CMAKE_USE_NSS OR CMAKE_USE_WOLFSSL)
   set(openssl_default OFF)
 endif()
 option(CMAKE_USE_OPENSSL "Use OpenSSL code. Experimental" ${openssl_default})
@@ -325,6 +326,7 @@ count_true(enabled_ssl_options_count
   CMAKE_USE_MBEDTLS
   CMAKE_USE_BEARSSL
   CMAKE_USE_NSS
+  CMAKE_USE_WOLFSSL
 )
 if(enabled_ssl_options_count GREATER "1")
   set(CURL_WITH_MULTI_SSL ON)
@@ -405,6 +407,14 @@ if(CMAKE_USE_BEARSSL)
   include_directories(${BEARSSL_INCLUDE_DIRS})
 endif()
 
+if(CMAKE_USE_WOLFSSL)
+  find_package(WolfSSL REQUIRED)
+  set(SSL_ENABLED ON)
+  set(USE_WOLFSSL ON)
+  list(APPEND CURL_LIBS ${WolfSSL_LIBRARIES})
+  include_directories(${WolfSSL_INCLUDE_DIRS})
+endif()
+
 if(CMAKE_USE_NSS)
   find_package(NSS REQUIRED)
   include_directories(${NSS_INCLUDE_DIRS})
@@ -750,7 +760,7 @@ elseif(CURL_CA_PATH_AUTODETECT OR CURL_CA_BUNDLE_AUTODETECT)
 endif()
 
 if(CURL_CA_PATH_SET AND NOT USE_OPENSSL AND NOT USE_MBEDTLS)
-  message(FATAL_ERROR
+  message(STATUS
           "CA path only supported by OpenSSL, GnuTLS or mbed TLS. "
           "Set CURL_CA_PATH=none or enable one of those TLS backends.")
 endif()
@@ -1311,6 +1321,7 @@ _add_if("Secure Transport" SSL_ENABLED AND USE_SECTRANSP)
 _add_if("mbedTLS"          SSL_ENABLED AND USE_MBEDTLS)
 _add_if("BearSSL"          SSL_ENABLED AND USE_BEARSSL)
 _add_if("NSS"              SSL_ENABLED AND USE_NSS)
+_add_if("wolfSSL"          SSL_ENABLED AND USE_WOLFSSL)
 if(_items)
   list(SORT _items)
 endif()

Makefile.am

@@ -5,7 +5,7 @@
 #                            | (__| |_| |  _ <| |___
 #                             \___|\___/|_| \_\_____|
 #
-# Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+# Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
 #
 # This software is licensed as described in the file COPYING, which
 # you should have received as part of this distribution. The terms
@@ -24,14 +24,24 @@ AUTOMAKE_OPTIONS = foreign
 
 ACLOCAL_AMFLAGS = -I m4
 
-CMAKE_DIST = CMakeLists.txt CMake/CMakeConfigurableFile.in      \
- CMake/CurlTests.c CMake/FindGSS.cmake CMake/OtherTests.cmake   \
- CMake/Platforms/WindowsCache.cmake CMake/Utilities.cmake       \
- CMake/Macros.cmake              \
- CMake/CurlSymbolHiding.cmake CMake/FindCARES.cmake             \
- CMake/FindLibSSH2.cmake CMake/FindNGHTTP2.cmake                \
- CMake/FindMbedTLS.cmake CMake/FindBearSSL.cmake                \
- CMake/cmake_uninstall.cmake.in CMake/curl-config.cmake.in
+CMAKE_DIST =                                    \
+ CMake/cmake_uninstall.cmake.in                 \
+ CMake/CMakeConfigurableFile.in                 \
+ CMake/curl-config.cmake.in                     \
+ CMake/CurlSymbolHiding.cmake                   \
+ CMake/CurlTests.c                              \
+ CMake/FindBearSSL.cmake                        \
+ CMake/FindCARES.cmake                          \
+ CMake/FindGSS.cmake                            \
+ CMake/FindLibSSH2.cmake                        \
+ CMake/FindMbedTLS.cmake                        \
+ CMake/FindNGHTTP2.cmake                        \
+ CMake/FindWolfSSL.cmake                        \
+ CMake/Macros.cmake                             \
+ CMake/OtherTests.cmake                         \
+ CMake/Platforms/WindowsCache.cmake             \
+ CMake/Utilities.cmake                          \
+ CMakeLists.txt
 
 VC6_LIBTMPL = projects/Windows/VC6/lib/libcurl.tmpl
 VC6_LIBDSP = projects/Windows/VC6/lib/libcurl.dsp.dist

lib/curl_config.h.cmake

@@ -945,6 +945,9 @@ ${SIZEOF_TIME_T_CODE}
 /* if BearSSL is enabled */
 #cmakedefine USE_BEARSSL 1
 
+/* if WolfSSL is enabled */
+#cmakedefine USE_WOLFSSL 1
+
 /* if libSSH2 is in use */
 #cmakedefine USE_LIBSSH2 1