cmake: auto detection of CURL_CA_BUNDLE/CURL_CA_PATH

Closes #1461

CMakeLists.txt

@@ -633,22 +633,65 @@ set(CURL_CA_FALLBACK OFF CACHE BOOL
 set(CURL_CA_PATH "auto" CACHE STRING
     "Location of default CA path. Set 'none' to disable or 'auto' for auto-detection. Defaults to 'auto'.")
 
-if("${CURL_CA_BUNDLE}" STREQUAL "none")
+if("${CURL_CA_BUNDLE}" STREQUAL "")
+    message(FATAL_ERROR "Invalid value of CURL_CA_BUNDLE. Use 'none', 'auto' or file path.")
+elseif("${CURL_CA_BUNDLE}" STREQUAL "none")
     unset(CURL_CA_BUNDLE CACHE)
 elseif("${CURL_CA_BUNDLE}" STREQUAL "auto")
-    # TODO: implement
-    message(SEND_ERROR "Auto mode not implemented for CURL_CA_BUNDLE")
-elseif("${CURL_CA_BUNDLE}" STREQUAL "")
-    message(SEND_ERROR "Invalid value of CURL_CA_BUNDLE. Use 'none', 'auto' or path.")
+    unset(CURL_CA_BUNDLE CACHE)
+    set(CURL_CA_BUNDLE_AUTODETECT TRUE)
+else()
+    set(CURL_CA_BUNDLE_SET TRUE)
 endif()
 
-if("${CURL_CA_PATH}" STREQUAL "none")
+if("${CURL_CA_PATH}" STREQUAL "")
+    message(FATAL_ERROR "Invalid value of CURL_CA_PATH. Use 'none', 'auto' or directory path.")
+elseif("${CURL_CA_PATH}" STREQUAL "none")
     unset(CURL_CA_PATH CACHE)
 elseif("${CURL_CA_PATH}" STREQUAL "auto")
-    # TODO: implement
-    message(SEND_ERROR "Auto mode not implemented for CURL_CA_PATH")
-elseif("${CURL_CA_PATH}" STREQUAL "")
-    message(SEND_ERROR "Invalid value of CURL_CA_PATH. Use 'none', 'auto' or path.")
+    unset(CURL_CA_PATH CACHE)
+    set(CURL_CA_PATH_AUTODETECT TRUE)
+else()
+    set(CURL_CA_PATH_SET TRUE)
+endif()
+
+if(CURL_CA_BUNDLE_SET AND CURL_CA_PATH_AUTODETECT)
+    # Skip autodetection of unset CA path because CA bundle is set explicitly
+elseif(CURL_CA_PATH_SET AND CURL_CA_BUNDLE_AUTODETECT)
+    # Skip autodetection of unset CA bundle because CA path is set explicitly
+elseif(CURL_CA_PATH_AUTODETECT OR CURL_CA_BUNDLE_AUTODETECT)
+    # first try autodetecting a CA bundle, then a CA path
+
+    if(CURL_CA_BUNDLE_AUTODETECT)
+        set(SEARCH_CA_BUNDLE_PATHS
+            /etc/ssl/certs/ca-certificates.crt
+            /etc/pki/tls/certs/ca-bundle.crt
+            /usr/share/ssl/certs/ca-bundle.crt
+            /usr/local/share/certs/ca-root-nss.crt
+            /etc/ssl/cert.pem)
+
+        foreach(SEARCH_CA_BUNDLE_PATH ${SEARCH_CA_BUNDLE_PATHS})
+            if(EXISTS "${SEARCH_CA_BUNDLE_PATH}")
+                message(STATUS "Found CA bundle: ${SEARCH_CA_BUNDLE_PATH}")
+                set(CURL_CA_BUNDLE "${SEARCH_CA_BUNDLE_PATH}")
+                set(CURL_CA_BUNDLE_SET TRUE CACHE)
+                break()
+            endif()
+        endforeach()
+    endif()
+
+    if(CURL_CA_PATH_AUTODETECT AND (NOT CURL_CA_PATH_SET))
+        if(EXISTS "/etc/ssl/certs")
+            set(CURL_CA_PATH "/etc/ssl/certs")
+            set(CURL_CA_PATH_SET TRUE CACHE)
+        endif()
+    endif()
+endif()
+
+if(CURL_CA_PATH_SET AND NOT (USE_OPENSSL OR GNUTLS_ENABLED))
+    message(FATAL_ERROR
+            "CA path only supported by OpenSSL, GnuTLS or PolarSSL. "
+            "Set CURL_CA_PATH=none or enable one of those TLS backends.")
 endif()