diff --git a/mon/antietcd_adapter.js b/mon/antietcd_adapter.js
index 83d879eb..a3f439e4 100644
--- a/mon/antietcd_adapter.js
+++ b/mon/antietcd_adapter.js
@@ -49,6 +49,17 @@ class AntiEtcdAdapter
                     stale_read: 1,
                     log_level: 1,
                 };
+                if (config.use_auth)
+                {
+                    antietcd_config.client_cert_auth = true;
+                    antietcd_config.auth_filter = require('./vitastor_auth_filter.js');
+                    antietcd_config.peer_ca = config.antietcd_server_ca;
+                    if (!config.antietcd_server_ca || config.antietcd_server_ca == config.etcd_ca)
+                    {
+                        console.error('Secure setup requires separate antietcd_server_ca (for signing antietcd server certificates) and etcd_ca (for signing client certificates)');
+                        process.exit(1);
+                    }
+                }
                 for (const key in config)
                 {
                     if (key.substr(0, 9) === 'antietcd_')
@@ -173,7 +184,7 @@ class AntiEtcdAdapter
                     await new Promise(ok => setTimeout(ok, timeout-(Date.now()-prev)));
                 }
                 prev = Date.now();
-                const res = await this.antietcd.api(path.replace(/^\/+/, '').replace(/\/+$/, '').replace(/\/+/g, '_'), body);
+                const res = await this.antietcd.api(path.replace(/^\/+/, '').replace(/\/+$/, '').replace(/\/+/g, '_'), body, { username: 'root' });
                 if (res.error)
                 {
                     console.error('Failed to query antietcd '+path+' (retry '+retry+'/'+retries+'): '+res.error);
diff --git a/mon/vitastor_auth_filter.js b/mon/vitastor_auth_filter.js
new file mode 100644
index 00000000..83264c76
--- /dev/null
+++ b/mon/vitastor_auth_filter.js
@@ -0,0 +1,471 @@
+// AntiEtcd authentication filter for Vitastor
+// (c) Vitaliy Filippov, 2026
+// License: Mozilla Public License 2.0 or Vitastor Network Public License 1.1
+
+// Permissions are based on:
+// 1. Users.
+//    Stored in /vitastor/config/user/<username>.
+//    Has 2 properties:
+//    - type, one of: osd, mon, admin, client.
+//      osd, mon types should be used by OSDs/monitors.
+//      admin should be used for administrative access from vitastor-cli.
+//      client should be used for regular clients.
+//    - groups, a list of group names the user is included in.
+// 2. Images.
+//    Stored in /vitastor/config/inode/<pool>/<inode>. Has the following properties:
+//    - owner (user name)
+//    - owner_group (group name)
+//    - reader_group
+
+const static_perms = {
+    invalid: {
+        keys: {},
+        prefixes: {},
+    },
+    osd: {
+        keys: { '/pg/config': false },
+        prefixes: { '/osd/': true, '/pg/state/': true, '/pg/history/': true, '/pgstats/': true },
+    },
+    mon: {
+        keys: { '/pg/config': true, '/stats': true, '/history/last_clean_pgs': true },
+        prefixes: {
+            '/config/': false, '/osd/': false, '/mon/': true, '/pg/history/': true,
+            '/pgstats/': false, '/inode/stats/': true, '/pool/stats/': true,
+        },
+    },
+    admin: {
+        keys: { '/stats': false },
+        prefixes: {
+            '/config/': true, '/osd/': true, '/index/': true, '/pg/history/': true,
+            '/mon/': false, '/pg/': false, '/pgstats/': false, '/inode/stats/': false, '/pool/stats/': false,
+        },
+    },
+    client: {
+        keys: { '/config/global': false, '/config/node_placement': false, '/config/pools': false, '/pg/config': false },
+        prefixes: { '/osd/stats/': false, '/pg/state/': false, '/index/maxid/': false },
+    },
+};
+
+const api_perms = {
+    osd: { lease_grant: true, lease_revoke: true, lease_keepalive: true },
+    mon: { lease_grant: true, lease_revoke: true, lease_keepalive: true },
+    admin: { maintenance_status: true },
+    client: {},
+};
+
+class VitastorAuthFilter
+{
+    constructor(antietcd)
+    {
+        this.cfg = antietcd.cfg;
+        this.antietcd = antietcd;
+        this.prefix = this.cfg.vitastor_prefix || '/vitastor';
+        this.prefix_parts = this.prefix.split('/');
+    }
+
+    _get(path, decode)
+    {
+        let cur = this.antietcd.etctree.state;
+        path = path instanceof Array ? path : path.split('/');
+        for (const p of path)
+        {
+            if (!cur.children)
+            {
+                return null;
+            }
+            cur = cur.children[p];
+            if (!cur)
+            {
+                return null;
+            }
+        }
+        if (decode)
+        {
+            return this._decode(path, cur.value);
+        }
+        return cur;
+    }
+
+    _decode(path, cur)
+    {
+        if (!cur)
+        {
+            return null;
+        }
+        if (cur)
+        {
+            try
+            {
+                cur = JSON.parse(cur);
+            }
+            catch (e)
+            {
+                console.warn('Invalid JSON in '+(path instanceof Array ? path.join('/') : path)+': '+e);
+            }
+        }
+        return cur;
+    }
+
+    // userInfo: { name: string, type: string, perms: static_perms[type], groups: { [string]: true } }
+    _check_compare(check, userInfo, checked)
+    {
+        let key = String(check.key);
+        if (key.substr(0, this.prefix.length) !== this.prefix)
+        {
+            return false;
+        }
+        key = key.substr(this.prefix.length);
+        if (key in userInfo.perms.keys)
+        {
+            return true;
+        }
+        for (const pfx in userInfo.perms.prefixes)
+        {
+            if (key.substr(0, pfx.length) == pfx)
+            {
+                return true;
+            }
+        }
+        if (userInfo.type == 'client')
+        {
+            // Image permissions
+            if (key.substr(0, 14) == '/config/inode/')
+            {
+                // Allowed to check that a key does not exist
+                if (check.target == 'VERSION' && check.version == 0)
+                {
+                    checked['M'+key] = true;
+                    return true;
+                }
+                else if (check.target == 'MOD')
+                {
+                    const data = this._get(check.key);
+                    if (!data || data.mod_revision != check.mod_revision)
+                    {
+                        // Break check to trigger CAS failure
+                        check.mod_revision = '18446744073709551615'; // UINT64_MAX
+                        return true;
+                    }
+                    const inode = this._decode(check.key, data.value);
+                    if (inode && (inode.owner_group && userInfo.groups[inode.owner_group] ||
+                        inode.owner === userInfo.name))
+                    {
+                        checked['M'+key] = true;
+                        return true;
+                    }
+                }
+                return false;
+            }
+            if (key.substr(0, 13) == '/index/image/')
+            {
+                // Allowed to check that a key does not exist
+                if (check.target == 'VERSION' && check.version == 0)
+                {
+                    checked['M'+key] = true;
+                    return true;
+                }
+                else if (check.target == 'MOD')
+                {
+                    let data = this._get(check.key);
+                    if (!data || data.mod_revision != check.mod_revision)
+                    {
+                        // Break check to trigger CAS failure
+                        check.mod_revision = '18446744073709551615'; // UINT64_MAX
+                        return true;
+                    }
+                    data = this._decode(check.key, data.value);
+                    if (data)
+                    {
+                        const inode = this._get([ ...this.prefix_parts, 'config', 'inode', data.pool_id, data.id ], true);
+                        if (inode && (inode.owner_group && userInfo.groups[inode.owner_group] ||
+                            inode.owner === userInfo.name))
+                        {
+                            checked['M'+key] = true;
+                            return true;
+                        }
+                    }
+                }
+                return false;
+            }
+            if (key.substr(0, 13) == '/index/maxid/')
+            {
+                const pool_id = key.substr(13);
+                const pool_cfg = this._get([ ...this.prefix_parts, 'config', 'pools' ], true);
+                if (!pool_cfg || !pool_cfg[pool_id] || !pool_cfg[pool_id].creator_group || !userInfo.groups[pool_cfg[pool_id].creator_group])
+                {
+                    return false;
+                }
+                if (check.target == 'VERSION' && check.version == 0)
+                {
+                    checked['I'+parseInt(key.substr(13))+'_0'] = true;
+                    return true;
+                }
+                else if (check.target == 'MOD')
+                {
+                    const data = this._get(check.key);
+                    if (!data || data.mod_revision != check.mod_revision)
+                    {
+                        // Break check to trigger CAS failure
+                        check.mod_revision = '18446744073709551615'; // UINT64_MAX
+                        return true;
+                    }
+                    checked['I'+parseInt(key.substr(13))+'_'+data.value] = true;
+                    return true;
+                }
+                return false;
+            }
+        }
+        return false;
+    }
+
+    _check_read(kv, userInfo)
+    {
+        let key = String(kv.key);
+        if (key.substr(0, this.prefix.length) !== this.prefix)
+        {
+            return false;
+        }
+        key = key.substr(this.prefix.length);
+        if (key in userInfo.perms.keys)
+        {
+            return true;
+        }
+        for (const pfx in userInfo.perms.prefixes)
+        {
+            if (key.substr(0, pfx.length) == pfx)
+            {
+                return true;
+            }
+        }
+        if (userInfo.type == 'client')
+        {
+            // Image permissions
+            if (key.substr(0, 14) == '/config/inode/')
+            {
+                const inode = this._decode(kv.key, kv.value);
+                if (inode && (inode.reader_group && userInfo.groups[inode.reader_group] ||
+                    inode.owner_group && userInfo.groups[inode.owner_group] ||
+                    inode.owner === userInfo.name))
+                {
+                    return true;
+                }
+                return false;
+            }
+            if (key.substr(0, 13) == '/index/image/')
+            {
+                const data = this._decode(kv.key, kv.value);
+                const inode = this._get([ ...this.prefix_parts, 'config', 'inode', data.pool_id, data.id ], true);
+                if (inode && (inode.reader_group && userInfo.groups[inode.reader_group] ||
+                    inode.owner_group && userInfo.groups[inode.owner_group] ||
+                    inode.owner === userInfo.name))
+                {
+                    return true;
+                }
+                return false;
+            }
+        }
+        return false;
+    }
+
+    _check_write(put, userInfo, checked)
+    {
+        let key = String(put.key);
+        if (key.substr(0, this.prefix.length) !== this.prefix)
+        {
+            return false;
+        }
+        key = key.substr(this.prefix.length);
+        if (userInfo.perms.keys[key])
+        {
+            return true;
+        }
+        for (const pfx in userInfo.perms.prefixes)
+        {
+            if (userInfo.perms.prefixes[pfx] && key.substr(0, pfx.length) == pfx)
+            {
+                return true;
+            }
+        }
+        if (checked && userInfo.type == 'client')
+        {
+            if (key.substr(0, 13) == '/index/maxid/' &&
+                checked['I'+parseInt(key.substr(13))+'_'+(put.value-1)])
+            {
+                // Allowed to increment maxid
+                return true;
+            }
+            if (checked['M'+key])
+            {
+                // Allowed to modify known images with CAS checks
+                return true;
+            }
+        }
+        return false;
+    }
+
+    _check_req(req, userInfo, checked)
+    {
+        let r;
+        if ((r = (req.request_range || req.requestRange)))
+        {
+            // All range queries are allowed, but responses are filtered - it's simpler
+        }
+        else if ((r = (req.request_put || req.requestPut)))
+        {
+            if (!this._check_write(r, userInfo, checked))
+                return false;
+        }
+        else if ((r = (req.request_delete_range || req.requestDeleteRange)))
+        {
+            if (!r.range_end || r.range_end === r.key)
+            {
+                if (!this._check_write({ key: r.key }, userInfo))
+                    return false;
+            }
+            else
+            {
+                // All keys in range must satisfy prefix
+                r.range_end = String(r.range_end);
+                if (r.key.length != r.range_end.length ||
+                    r.key[r.key.length-1] != '/' ||
+                    r.range_end[r.range_end.length-1] != '0')
+                {
+                    return false;
+                }
+                let key = r.key.substr(this.prefix.length);
+                let found = false;
+                for (const pfx in userInfo.perms.prefixes)
+                {
+                    if (userInfo.perms.prefixes[pfx] && key.substr(0, pfx.length) == pfx)
+                    {
+                        found = true;
+                        break;
+                    }
+                }
+                if (!found)
+                    return false;
+            }
+        }
+        return true;
+    }
+
+    _get_user(username)
+    {
+        if (!username)
+        {
+            return null;
+        }
+        let userInfo = this._get([ ...this.prefix_parts, 'config', 'user', username ], true);
+        if (!userInfo)
+        {
+            userInfo = { type: 'client' };
+        }
+        userInfo.perms = static_perms[userInfo.type] || static_perms['invalid'];
+        userInfo.name = username;
+        if (userInfo.groups instanceof Array)
+        {
+            userInfo.groups = userInfo.groups.reduce((a, c) => { a[c] = true; return a; }, {});
+        }
+        else
+        {
+            userInfo.groups = {};
+        }
+        return userInfo;
+    }
+
+    filter_api(username, api/*, data*/)
+    {
+        if (username === 'root')
+        {
+            return true;
+        }
+        const userInfo = this._get([ ...this.prefix_parts, 'config', 'user', username ], true);
+        return userInfo && api_perms[userInfo.type] && api_perms[userInfo.type][api];
+    }
+
+    filter_txn(username, txn)
+    {
+        if (username === 'root')
+        {
+            return true;
+        }
+        const userInfo = this._get_user(username);
+        if (!userInfo)
+        {
+            return null;
+        }
+        const checked = {};
+        if (txn.compare)
+        {
+            for (const check of txn.compare)
+            {
+                if (!this._check_compare(check, userInfo, checked))
+                    return null;
+            }
+        }
+        // Special transactions:
+        // 1. create image: create config/inode and index/image, increment index/maxid/<pool> (with CAS)
+        // 2. create snapshot: same as create image but also rename previous to @snap
+        if (txn.success)
+        {
+            for (const req of txn.success)
+            {
+                if (!this._check_req(req, userInfo, checked))
+                    return null;
+            }
+        }
+        if (txn.failure)
+        {
+            for (const req of txn.failure)
+            {
+                if (!this._check_req(req, userInfo, null))
+                    return null;
+            }
+        }
+        return txn;
+    }
+
+    filter_txn_response(username, txn, res)
+    {
+        if (!res.responses || username === 'root')
+        {
+            return;
+        }
+        const userInfo = this._get_user(username);
+        if (!userInfo)
+        {
+            for (const resp of res.responses)
+            {
+                if (resp.response_range && resp.response_range.kvs)
+                {
+                    resp.response_range.kvs = [];
+                }
+            }
+            return;
+        }
+        for (const resp of res.responses)
+        {
+            if (resp.response_range && resp.response_range.kvs)
+            {
+                resp.response_range.kvs = resp.response_range.kvs.filter(kv => this._check_read(kv, userInfo));
+            }
+        }
+    }
+
+    filter_watch_message(username, msg)
+    {
+        if (!msg.result || !msg.result.events || username === 'root')
+        {
+            return;
+        }
+        const userInfo = this._get_user(username);
+        if (!userInfo)
+        {
+            msg.result.events = [];
+            return;
+        }
+        msg.result.events = msg.result.events.filter(ev => this._check_read(ev.kv, userInfo));
+    }
+}
+
+module.exports = VitastorAuthFilter;