OPENJDK-2108: Internal __redhat_fips__ property

Introduce an 'include'-directives-only __redhat_fips__ magic property
that expands as either true or false depending on the System FIPS
status, reported by the /proc/sys/crypto/fips_enabled kernel file.

Author: franferrax

src/java.base/share/classes/sun/security/util/PropertyExpander.java

@@ -61,12 +61,35 @@ public static String expand(String value, boolean encodeURL)
         return expand(value, encodeURL, System::getProperty);
     }
 
+    /* vvvvvvvvvvvvvvvvvvvvvvvvvvvvv FIPS PATCH vvvvvvvvvvvvvvvvvvvvvvvvvvvvv */
+    private static final class RedHatFIPS {
+        // This 'include'-directives-only magic property is an internal
+        // implementation detail that could (and probably will!) change.
+        // Red Hat customers should NOT rely on this for their own use.
+        private static final String MAGIC_PROP = "__redhat_fips__";
+        private static final String IS_ON = "" + isOn();
+
+        private static boolean isOn() {
+            String path = "/proc/sys/crypto/fips_enabled";
+            try (java.io.InputStream is = new java.io.FileInputStream(path)) {
+                return is.read() == '1';
+            } catch (java.io.IOException ignore) {
+                return false;
+            }
+        }
+
+        static String getProperty(String key) {
+            return MAGIC_PROP.equals(key) ? IS_ON : System.getProperty(key, "");
+        }
+    }
+    /* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ FIPS PATCH ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ */
+
     /*
      * In non-strict mode an undefined property is replaced by an empty string.
      */
     public static String expandNonStrict(String value) {
         try {
-            return expand(value, false, key -> System.getProperty(key, ""));
+            return expand(value, false, RedHatFIPS::getProperty); //< FIPS PATCH
         } catch (ExpandException e) {
             // should not happen
             throw new AssertionError("unexpected expansion error: when " +