diff --git a/web/src/app/Api.js b/web/src/app/Api.js
index 8bb7770..471b410 100644
--- a/web/src/app/Api.js
+++ b/web/src/app/Api.js
@@ -1,4 +1,4 @@
-import {topicUrlJsonPoll, fetchLinesIterator, topicUrl} from "./utils";
+import {topicUrlJsonPoll, fetchLinesIterator, topicUrl, topicUrlAuth} from "./utils";
 
 class Api {
     async poll(baseUrl, topic) {
@@ -19,6 +19,20 @@ class Api {
             body: message
         });
     }
+
+    async auth(baseUrl, topic, user) {
+        const url = topicUrlAuth(baseUrl, topic);
+        console.log(`[Api] Checking auth for ${url}`);
+        const response = await fetch(url);
+        if (response.status >= 200 && response.status <= 299) {
+            return true;
+        } else if (!user && response.status === 404) {
+            return true; // Special case: Anonymous login to old servers return 404 since /<topic>/auth doesn't exist
+        } else if (response.status === 401 || response.status === 403) { // See server/server.go
+            return false;
+        }
+        throw new Error(`Unexpected server response ${response.status}`);
+    }
 }
 
 const api = new Api();
diff --git a/web/src/app/Subscriptions.js b/web/src/app/Subscriptions.js
index 916da3a..78a9ef8 100644
--- a/web/src/app/Subscriptions.js
+++ b/web/src/app/Subscriptions.js
@@ -10,8 +10,7 @@ class Subscriptions {
 
     get(subscriptionId) {
         const subscription = this.subscriptions.get(subscriptionId);
-        if (subscription === undefined) return null;
-        return subscription;
+        return (subscription) ? subscription : null;
     }
 
     update(subscription) {
@@ -38,8 +37,7 @@ class Subscriptions {
 
     firstOrNull() {
         const first = this.subscriptions.values().next().value;
-        if (first === undefined) return null;
-        return first;
+        return (first) ? first : null;
     }
 
     size() {
diff --git a/web/src/app/utils.js b/web/src/app/utils.js
index 416be6d..40b9f56 100644
--- a/web/src/app/utils.js
+++ b/web/src/app/utils.js
@@ -7,6 +7,7 @@ export const topicUrlWs = (baseUrl, topic) => `${topicUrl(baseUrl, topic)}/ws`
 export const topicUrlWsWithSince = (baseUrl, topic, since) => `${topicUrlWs(baseUrl, topic)}?since=${since}`;
 export const topicUrlJson = (baseUrl, topic) => `${topicUrl(baseUrl, topic)}/json`;
 export const topicUrlJsonPoll = (baseUrl, topic) => `${topicUrlJson(baseUrl, topic)}?poll=1`;
+export const topicUrlAuth = (baseUrl, topic) => `${topicUrl(baseUrl, topic)}/auth`;
 export const shortUrl = (url) => url.replaceAll(/https?:\/\//g, "");
 export const shortTopicUrl = (baseUrl, topic) => shortUrl(topicUrl(baseUrl, topic));
 
diff --git a/web/src/components/NotificationList.js b/web/src/components/NotificationList.js
index 3c3cc75..9facfb7 100644
--- a/web/src/components/NotificationList.js
+++ b/web/src/components/NotificationList.js
@@ -1,9 +1,9 @@
 import Container from "@mui/material/Container";
-import {CardContent, CardHeader, Stack} from "@mui/material";
+import {CardContent, Stack} from "@mui/material";
 import Card from "@mui/material/Card";
 import Typography from "@mui/material/Typography";
 import * as React from "react";
-import {formatTitle, formatMessage, unmatchedTags} from "../app/utils";
+import {formatMessage, formatTitle, unmatchedTags} from "../app/utils";
 import IconButton from "@mui/material/IconButton";
 import CloseIcon from '@mui/icons-material/Close';
 
diff --git a/web/src/components/SubscribeDialog.js b/web/src/components/SubscribeDialog.js
index 1a8388f..55240c7 100644
--- a/web/src/components/SubscribeDialog.js
+++ b/web/src/components/SubscribeDialog.js
@@ -8,47 +8,110 @@ import DialogContentText from '@mui/material/DialogContentText';
 import DialogTitle from '@mui/material/DialogTitle';
 import {useState} from "react";
 import Subscription from "../app/Subscription";
+import {useMediaQuery} from "@mui/material";
+import theme from "./theme";
+import api from "../app/Api";
+import {topicUrl} from "../app/utils";
 
 const defaultBaseUrl = "http://127.0.0.1"
 //const defaultBaseUrl = "https://ntfy.sh"
 
 const SubscribeDialog = (props) => {
+    const [baseUrl, setBaseUrl] = useState(defaultBaseUrl); // FIXME
     const [topic, setTopic] = useState("");
+    const [showLoginPage, setShowLoginPage] = useState(false);
+    const fullScreen = useMediaQuery(theme.breakpoints.down('sm'));
     const handleCancel = () => {
         setTopic('');
         props.onCancel();
     }
-    const handleSubmit = () => {
+    const handleSubmit = async () => {
+        const success = await api.auth(baseUrl, topic, null);
+        if (!success) {
+            console.log(`[SubscribeDialog] Login required for ${topicUrl(baseUrl, topic)}`)
+            setShowLoginPage(true);
+            return;
+        }
         const subscription = new Subscription(defaultBaseUrl, topic);
         props.onSubmit(subscription);
         setTopic('');
     }
+    return (
+        <Dialog open={props.open} onClose={props.onClose} fullScreen={fullScreen}>
+            {!showLoginPage && <SubscribePage
+                topic={topic}
+                setTopic={setTopic}
+                onCancel={handleCancel}
+                onSubmit={handleSubmit}
+            />}
+            {showLoginPage && <LoginPage
+                topic={topic}
+                onBack={() => setShowLoginPage(false)}
+            />}
+        </Dialog>
+    );
+};
+
+const SubscribePage = (props) => {
     return (
         <>
-            <Dialog open={props.open} onClose={props.onClose}>
-                <DialogTitle>Subscribe to topic</DialogTitle>
-                <DialogContent>
-                    <DialogContentText>
-                        Topics may not be password-protected, so choose a name that's not easy to guess.
-                        Once subscribed, you can PUT/POST notifications.
-                    </DialogContentText>
-                    <TextField
-                        autoFocus
-                        margin="dense"
-                        id="name"
-                        label="Topic name, e.g. phil_alerts"
-                        value={topic}
-                        onChange={ev => setTopic(ev.target.value)}
-                        type="text"
-                        fullWidth
-                        variant="standard"
-                    />
-                </DialogContent>
-                <DialogActions>
-                    <Button onClick={handleCancel}>Cancel</Button>
-                    <Button onClick={handleSubmit} autoFocus disabled={topic === ""}>Subscribe</Button>
-                </DialogActions>
-            </Dialog>
+            <DialogTitle>Subscribe to topic</DialogTitle>
+            <DialogContent>
+                <DialogContentText>
+                    Topics may not be password-protected, so choose a name that's not easy to guess.
+                    Once subscribed, you can PUT/POST notifications.
+                </DialogContentText>
+                <TextField
+                    autoFocus
+                    margin="dense"
+                    id="topic"
+                    label="Topic name, e.g. phil_alerts"
+                    value={props.topic}
+                    onChange={ev => props.setTopic(ev.target.value)}
+                    type="text"
+                    fullWidth
+                    variant="standard"
+                />
+            </DialogContent>
+            <DialogActions>
+                <Button onClick={props.onCancel}>Cancel</Button>
+                <Button onClick={props.onSubmit} disabled={props.topic === ""}>Subscribe</Button>
+            </DialogActions>
+        </>
+    );
+};
+
+const LoginPage = (props) => {
+    return (
+        <>
+            <DialogTitle>Login required</DialogTitle>
+            <DialogContent>
+                <DialogContentText>
+                    This topic is password-protected. Please enter username and
+                    password to subscribe.
+                </DialogContentText>
+                <TextField
+                    autoFocus
+                    margin="dense"
+                    id="username"
+                    label="Username, e.g. phil"
+                    type="text"
+                    fullWidth
+                    variant="standard"
+                />
+                <TextField
+                    margin="dense"
+                    id="password"
+                    label="Password"
+                    type="password"
+                    fullWidth
+                    variant="standard"
+                />
+            </DialogContent>
+            <DialogActions>
+                <Button onClick={props.onBack}>Back</Button>
+                <Button>Login</Button>
+            </DialogActions>
         </>
     );
 };