diff --git a/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthProvider.java b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthProvider.java
index d519757..57859d7 100644
--- a/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthProvider.java
+++ b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthProvider.java
@@ -20,16 +20,41 @@
 
 package io.kamax.mxisd.backend.rest;
 
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import io.kamax.matrix.MatrixID;
+import io.kamax.matrix._MatrixID;
 import io.kamax.mxisd.auth.UserAuthResult;
 import io.kamax.mxisd.auth.provider.AuthenticatorProvider;
 import io.kamax.mxisd.config.rest.RestBackendConfig;
-import org.apache.commons.lang.NotImplementedException;
+import io.kamax.mxisd.util.GsonParser;
+import io.kamax.mxisd.util.RestClientUtils;
+import org.apache.http.client.methods.CloseableHttpResponse;
+import org.apache.http.client.methods.HttpUriRequest;
+import org.apache.http.impl.client.CloseableHttpClient;
+import org.apache.http.impl.client.HttpClients;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
 
+import java.io.IOException;
+
+@Component
 public class RestAuthProvider implements AuthenticatorProvider {
 
-    @Autowired
     private RestBackendConfig cfg;
+    private Gson gson;
+    private GsonParser parser;
+    private CloseableHttpClient client;
+
+    @Autowired
+    public RestAuthProvider(RestBackendConfig cfg) {
+        this.cfg = cfg;
+
+        client = HttpClients.createDefault();
+        gson = new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create();
+        parser = new GsonParser(gson);
+    }
 
     @Override
     public boolean isEnabled() {
@@ -38,7 +63,31 @@ public class RestAuthProvider implements AuthenticatorProvider {
 
     @Override
     public UserAuthResult authenticate(String id, String password) {
-        throw new NotImplementedException();
+        _MatrixID mxid = new MatrixID(id);
+        RestAuthRequestJson auth = new RestAuthRequestJson();
+        auth.setMxid(id);
+        auth.setLocalpart(mxid.getLocalPart());
+        auth.setDomain(mxid.getDomain());
+        auth.setPassword(password);
+
+        HttpUriRequest req = RestClientUtils.post(cfg.getEndpoints().getAuth(), gson, "auth", auth);
+        try (CloseableHttpResponse res = client.execute(req)) {
+            UserAuthResult result = new UserAuthResult();
+
+            int status = res.getStatusLine().getStatusCode();
+            if (status < 200 || status >= 300) {
+                return result.failure();
+            }
+
+            RestAuthReplyJson reply = parser.parse(res, "auth", RestAuthReplyJson.class);
+            if (!reply.isSuccess()) {
+                return result.failure();
+            }
+
+            return result.success(reply.getMxid(), reply.getProfile().getDisplayName());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
     }
 
 }
diff --git a/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthReplyJson.java b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthReplyJson.java
new file mode 100644
index 0000000..cb0cef7
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthReplyJson.java
@@ -0,0 +1,81 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.backend.rest;
+
+import io.kamax.mxisd.ThreePid;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RestAuthReplyJson {
+
+    public static class RestAuthProfileData {
+
+        private String displayName;
+        private List<ThreePid> threePids = new ArrayList<>();
+
+        public String getDisplayName() {
+            return displayName;
+        }
+
+        public void setDisplayName(String displayName) {
+            this.displayName = displayName;
+        }
+
+        public List<ThreePid> getThreePids() {
+            return threePids;
+        }
+
+        public void setThreePids(List<ThreePid> threePids) {
+            this.threePids = threePids;
+        }
+
+    }
+
+    private Boolean success;
+    private String mxid;
+    private RestAuthProfileData profile;
+
+    public boolean isSuccess() {
+        return success;
+    }
+
+    public void setSuccess(boolean success) {
+        this.success = success;
+    }
+
+    public String getMxid() {
+        return mxid;
+    }
+
+    public void setMxid(String mxid) {
+        this.mxid = mxid;
+    }
+
+    public RestAuthProfileData getProfile() {
+        return profile;
+    }
+
+    public void setProfile(RestAuthProfileData profile) {
+        this.profile = profile;
+    }
+
+}
diff --git a/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthRequestJson.java b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthRequestJson.java
new file mode 100644
index 0000000..92d0a5a
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/backend/rest/RestAuthRequestJson.java
@@ -0,0 +1,62 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.backend.rest;
+
+public class RestAuthRequestJson {
+
+    private String mxid;
+    private String localpart;
+    private String domain;
+    private String password;
+
+    public String getMxid() {
+        return mxid;
+    }
+
+    public void setMxid(String mxid) {
+        this.mxid = mxid;
+    }
+
+    public String getLocalpart() {
+        return localpart;
+    }
+
+    public void setLocalpart(String localpart) {
+        this.localpart = localpart;
+    }
+
+    public String getDomain() {
+        return domain;
+    }
+
+    public void setDomain(String domain) {
+        this.domain = domain;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+
+}
diff --git a/src/main/groovy/io/kamax/mxisd/exception/InvalidResponseJsonException.java b/src/main/groovy/io/kamax/mxisd/exception/InvalidResponseJsonException.java
new file mode 100644
index 0000000..fde88e4
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/exception/InvalidResponseJsonException.java
@@ -0,0 +1,29 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.exception;
+
+public class InvalidResponseJsonException extends RuntimeException {
+
+    public InvalidResponseJsonException(String s) {
+        super(s);
+    }
+
+}
diff --git a/src/main/groovy/io/kamax/mxisd/util/GsonParser.java b/src/main/groovy/io/kamax/mxisd/util/GsonParser.java
new file mode 100644
index 0000000..c528f5c
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/util/GsonParser.java
@@ -0,0 +1,73 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.util;
+
+import com.google.gson.*;
+import io.kamax.mxisd.exception.InvalidResponseJsonException;
+import org.apache.commons.io.IOUtils;
+import org.apache.http.HttpResponse;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+
+public class GsonParser {
+
+    private JsonParser parser = new JsonParser();
+    private Gson gson;
+
+    public GsonParser() {
+        this(new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create());
+    }
+
+    public GsonParser(Gson gson) {
+        this.gson = gson;
+    }
+
+    public JsonObject parse(InputStream stream, String property) throws IOException {
+        JsonElement el = parser.parse(IOUtils.toString(stream, StandardCharsets.UTF_8));
+        if (!el.isJsonObject()) {
+            throw new InvalidResponseJsonException("Response body is not a JSON object");
+        }
+
+        JsonObject obj = el.getAsJsonObject();
+        if (!obj.has(property)) {
+            throw new IOException("Member " + property + " does not exist");
+        }
+
+        el = obj.get(property);
+        if (!el.isJsonObject()) {
+            throw new InvalidResponseJsonException("Member " + property + " is not a JSON object");
+        }
+
+        return el.getAsJsonObject();
+    }
+
+    public <T> T parse(InputStream stream, String memberName, Class<T> type) throws IOException {
+        JsonObject obj = parse(stream, memberName);
+        return gson.fromJson(obj, type);
+    }
+
+    public <T> T parse(HttpResponse res, String memberName, Class<T> type) throws IOException {
+        return parse(res.getEntity().getContent(), memberName, type);
+    }
+
+}
diff --git a/src/main/groovy/io/kamax/mxisd/util/JsonUtils.java b/src/main/groovy/io/kamax/mxisd/util/JsonUtils.java
new file mode 100644
index 0000000..1edf26a
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/util/JsonUtils.java
@@ -0,0 +1,38 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.util;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonObject;
+
+public class JsonUtils {
+
+    public static JsonObject getObj(Gson gson, String property, Object value) {
+        JsonObject obj = new JsonObject();
+        obj.add(property, gson.toJsonTree(value));
+        return obj;
+    }
+
+    public static String getObjAsString(Gson gson, String property, Object value) {
+        return gson.toJson(getObj(gson, property, value));
+    }
+
+}
diff --git a/src/main/groovy/io/kamax/mxisd/util/RestClientUtils.java b/src/main/groovy/io/kamax/mxisd/util/RestClientUtils.java
new file mode 100644
index 0000000..23eaa2e
--- /dev/null
+++ b/src/main/groovy/io/kamax/mxisd/util/RestClientUtils.java
@@ -0,0 +1,44 @@
+/*
+ * mxisd - Matrix Identity Server Daemon
+ * Copyright (C) 2017 Maxime Dor
+ *
+ * https://max.kamax.io/
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.kamax.mxisd.util;
+
+import com.google.gson.Gson;
+import org.apache.http.client.methods.HttpPost;
+import org.apache.http.entity.ContentType;
+import org.apache.http.entity.StringEntity;
+
+import java.nio.charset.StandardCharsets;
+
+public class RestClientUtils {
+
+    public static HttpPost post(String url, String body) {
+        StringEntity entity = new StringEntity(body, StandardCharsets.UTF_8);
+        entity.setContentType(ContentType.APPLICATION_JSON.toString());
+        HttpPost req = new HttpPost(url);
+        req.setEntity(entity);
+        return req;
+    }
+
+    public static HttpPost post(String url, Gson gson, String member, Object o) {
+        return post(url, JsonUtils.getObjAsString(gson, member, o));
+    }
+
+}