GUACAMOLE-393: Add AuthenticationProvider shutdown hook.

extensions/guacamole-auth-cas/src/main/java/org/apache/guacamole/auth/cas/CASAuthenticationProvider.java

@@ -107,4 +107,9 @@ public class CASAuthenticationProvider implements AuthenticationProvider {
 
     }
 
+    @Override
+    public void shutdown() {
+        // Do nothing
+    }
+
 }

extensions/guacamole-auth-duo/src/main/java/org/apache/guacamole/auth/duo/DuoAuthenticationProvider.java

@@ -102,4 +102,9 @@ public class DuoAuthenticationProvider implements AuthenticationProvider {
         return context;
     }
 
+    @Override
+    public void shutdown() {
+        // Do nothing
+    }
+
 }

extensions/guacamole-auth-header/src/main/java/org/apache/guacamole/auth/header/HTTPHeaderAuthenticationProvider.java

@@ -107,4 +107,9 @@ public class HTTPHeaderAuthenticationProvider implements AuthenticationProvider
 
     }
 
+    @Override
+    public void shutdown() {
+        // Do nothing
+    }
+
 }

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/InjectedAuthenticationProvider.java

@@ -104,4 +104,9 @@ public abstract class InjectedAuthenticationProvider implements AuthenticationPr
                 authenticatedUser, credentials);
     }
 
+    @Override
+    public void shutdown() {
+        // Do nothing
+    }
+
 }

extensions/guacamole-auth-ldap/src/main/java/org/apache/guacamole/auth/ldap/LDAPAuthenticationProvider.java

@@ -103,5 +103,10 @@ public class LDAPAuthenticationProvider implements AuthenticationProvider {
         return context;
     }
 
+    @Override
+    public void shutdown() {
+        // Do nothing
+    }
+
 }