Experimental support for synapse REST auth module

- See https://github.com/maxidor/matrix-synapse-rest-auth
- Include Google Firebase backend using UID as login and user token as password

src/main/groovy/io/kamax/mxisd/auth/AuthManager.java

@@ -0,0 +1,35 @@
+package io.kamax.mxisd.auth;
+
+import io.kamax.mxisd.auth.provider.AuthenticatorProvider;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.ArrayList;
+import java.util.List;
+
+@Service
+public class AuthManager {
+
+    private Logger log = LoggerFactory.getLogger(AuthManager.class);
+
+    @Autowired
+    private List<AuthenticatorProvider> providers = new ArrayList<>();
+
+    public UserAuthResult authenticate(String id, String password) {
+        for (AuthenticatorProvider provider : providers) {
+            if (!provider.isEnabled()) {
+                continue;
+            }
+
+            UserAuthResult result = provider.authenticate(id, password);
+            if (result.isSuccess()) {
+                return result;
+            }
+        }
+
+        return new UserAuthResult().failure();
+    }
+
+}