diff --git a/.changeset/reverse-proxy-passkey.md b/.changeset/reverse-proxy-passkey.md
new file mode 100644
index 0000000..7ed7f7d
--- /dev/null
+++ b/.changeset/reverse-proxy-passkey.md
@@ -0,0 +1,8 @@
+---
+"emdash": patch
+"@emdash-cms/admin": patch
+---
+
+Adds `passkeyPublicOrigin` on `emdash()` so WebAuthn `origin` and `rpId` match the browser when dev sits behind a TLS-terminating reverse proxy. Validates the value at integration load time and threads it through all passkey-related API routes.
+
+Updates the admin passkey setup and login flows to detect non-secure origins and explain that passkeys need HTTPS or `http://localhost` rather than implying the browser lacks WebAuthn support.
diff --git a/demos/simple/astro.config.mjs b/demos/simple/astro.config.mjs
index e84e940..d775532 100644
--- a/demos/simple/astro.config.mjs
+++ b/demos/simple/astro.config.mjs
@@ -10,6 +10,13 @@ export default defineConfig({
 	adapter: node({
 		mode: "standalone",
 	}),
+	// Example: allowed domains for reverse proxy
+	// security: {
+	// 	allowedDomains: [
+	// 		{ hostname: "emdash.local", protocol: "http" },
+	// 		{ hostname: "emdash.local", protocol: "https" },
+	// 	],
+	// },
 	image: {
 		layout: "constrained",
 		responsiveStyles: true,
@@ -23,7 +30,15 @@ export default defineConfig({
 				baseUrl: "/_emdash/api/media/file",
 			}),
 			plugins: [auditLogPlugin()],
+			// HTTPS reverse proxy: uncomment so passkey verify matches browser origin
+			// passkeyPublicOrigin: "https://emdash.local:8443",
 		}),
 	],
 	devToolbar: { enabled: false },
+	// Example: allowed hosts for reverse proxy
+	// vite: {
+	// 	server: {
+	// 		allowedHosts: ["emdash.local"],
+	// 	},
+	// },
 });
diff --git a/docs/src/content/docs/reference/configuration.mdx b/docs/src/content/docs/reference/configuration.mdx
index dbe1e43..e1d5376 100644
--- a/docs/src/content/docs/reference/configuration.mdx
+++ b/docs/src/content/docs/reference/configuration.mdx
@@ -200,6 +200,67 @@ Use Cloudflare Access as the authentication provider instead of passkeys.
 	magic links, and self-signup are disabled.
 </Aside>
 
+### `passkeyPublicOrigin`
+
+**Optional.** Pass a full **browser-facing origin** (scheme + host + optional port, **no path**) so WebAuthn **`rpId`** and **`origin`** match what the user’s browser sends in `clientData.origin`.
+
+By default, passkeys follow **`Astro.url`** / **`request.url`**. Behind a **TLS-terminating reverse proxy**, the app often still sees **`http://`** on the internal hop while the tab is **`https://`**, or the reconstructed host does not match the public name — which breaks passkey verification. Set `passkeyPublicOrigin` to the origin users type in the address bar (for example `https://cms.example.com` or `https://cms.example.com:8443`).
+
+The integration **validates** this value at load time: it must be a valid URL with **`http:`** or **`https:`** protocol and is normalized to **`origin`**.
+
+```js
+emdash({
+	database: sqlite({ url: "file:./data.db" }),
+	storage: local({
+		directory: "./uploads",
+		baseUrl: "/_emdash/api/media/file",
+	}),
+	passkeyPublicOrigin: "https://cms.example.com",
+});
+```
+
+#### Reverse proxy and passkeys
+
+Astro only reflects **`X-Forwarded-*`** when the public host is allowed. Configure [**`security.allowedDomains`**](https://docs.astro.build/en/reference/configuration-reference/#securityalloweddomains) for the hostname (and schemes) your users hit. In **`astro dev`**, add matching **`vite.server.allowedHosts`** so Vite accepts the proxy **`Host`** header.
+
+Prefer fixing **`allowedDomains`** (and forwarded headers) first; use **`passkeyPublicOrigin`** when the reconstructed URL **still** diverges from the browser origin (typical when TLS is terminated in front and the upstream request stays **`http://`**).
+
+With TLS in front, binding the dev server to loopback (**`astro dev --host 127.0.0.1`**) is often enough: the proxy connects locally while **`passkeyPublicOrigin`** matches the public HTTPS origin.
+
+<Aside type="caution">
+	Your reverse proxy should forward a **port-aware** `Host` / `X-Forwarded-Host` when you use non-default ports. If the proxy strips the port, **`rpId`** and Astro’s rebuilt URL can be wrong.
+</Aside>
+
+```js title="astro.config.mjs (excerpt)"
+import { defineConfig } from "astro/config";
+import emdash, { local } from "emdash/astro";
+import { sqlite } from "emdash/db";
+
+export default defineConfig({
+	security: {
+		allowedDomains: [
+			{ hostname: "cms.example.com", protocol: "https" },
+			{ hostname: "cms.example.com", protocol: "http" },
+		],
+	},
+	vite: {
+		server: {
+			allowedHosts: ["cms.example.com"],
+		},
+	},
+	integrations: [
+		emdash({
+			database: sqlite({ url: "file:./data.db" }),
+			storage: local({
+				directory: "./uploads",
+				baseUrl: "/_emdash/api/media/file",
+			}),
+			passkeyPublicOrigin: "https://cms.example.com",
+		}),
+	],
+});
+```
+
 ## Database Adapters
 
 Import from `emdash/db`:
diff --git a/e2e/fixture/emdash-env.d.ts b/e2e/fixture/emdash-env.d.ts
index 55834d4..918ed35 100644
--- a/e2e/fixture/emdash-env.d.ts
+++ b/e2e/fixture/emdash-env.d.ts
@@ -3,7 +3,7 @@
 
 /// <reference types="emdash/locals" />
 
-import type { PortableTextBlock } from "emdash";
+import type { ContentBylineCredit, PortableTextBlock } from "emdash";
 
 export interface Page {
   id: string;
@@ -14,6 +14,7 @@ export interface Page {
   createdAt: Date;
   updatedAt: Date;
   publishedAt: Date | null;
+  bylines?: ContentBylineCredit[];
 }
 
 export interface Post {
@@ -28,6 +29,7 @@ export interface Post {
   createdAt: Date;
   updatedAt: Date;
   publishedAt: Date | null;
+  bylines?: ContentBylineCredit[];
 }
 
 declare module "emdash" {
diff --git a/e2e/fixtures/refresh-server-pat.ts b/e2e/fixtures/refresh-server-pat.ts
new file mode 100644
index 0000000..8fb56d0
--- /dev/null
+++ b/e2e/fixtures/refresh-server-pat.ts
@@ -0,0 +1,24 @@
+/**
+ * Re-runs dev-bypass after a dev-reset so the server info file has a valid PAT
+ * and the fixture database is back in "setup complete" state.
+ */
+import { readFileSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+const SERVER_INFO_PATH = join(tmpdir(), "emdash-pw-server.json");
+
+export async function refreshServerPatAfterDevBypass(baseUrl: string): Promise<void> {
+	const res = await fetch(`${baseUrl}/_emdash/api/setup/dev-bypass?token=1`);
+	if (!res.ok) {
+		throw new Error(`dev-bypass failed (${res.status}): ${await res.text()}`);
+	}
+	const json: { data: { token?: string } } = await res.json();
+	const token = json.data.token;
+	if (!token) throw new Error("dev-bypass did not return a PAT token");
+
+	// Update the server info so subsequent tests use the fresh token
+	const info = JSON.parse(readFileSync(SERVER_INFO_PATH, "utf-8"));
+	info.token = token;
+	writeFileSync(SERVER_INFO_PATH, JSON.stringify(info, null, 2));
+}
diff --git a/e2e/fixtures/virtual-authenticator.ts b/e2e/fixtures/virtual-authenticator.ts
new file mode 100644
index 0000000..e3d6aae
--- /dev/null
+++ b/e2e/fixtures/virtual-authenticator.ts
@@ -0,0 +1,33 @@
+/**
+ * Chrome DevTools virtual WebAuthn authenticator for passkey e2e.
+ * Chromium-only (CDP). See https://developer.chrome.com/docs/devtools/webauthn/
+ */
+import type { Page } from "@playwright/test";
+
+export async function addVirtualWebAuthnAuthenticator(page: Page): Promise<() => Promise<void>> {
+	const session = await page.context().newCDPSession(page);
+	await session.send("WebAuthn.enable");
+	const { authenticatorId } = await session.send("WebAuthn.addVirtualAuthenticator", {
+		options: {
+			protocol: "ctap2",
+			transport: "internal",
+			hasResidentKey: true,
+			hasUserVerification: true,
+			isUserVerified: true,
+			automaticPresenceSimulation: true,
+		},
+	});
+
+	return async () => {
+		try {
+			await session.send("WebAuthn.removeVirtualAuthenticator", { authenticatorId });
+		} catch {
+			// session may already be closed
+		}
+		try {
+			await session.detach();
+		} catch {
+			// ignore
+		}
+	};
+}
diff --git a/e2e/tests/passkey-full-setup-virtual-auth.spec.ts b/e2e/tests/passkey-full-setup-virtual-auth.spec.ts
new file mode 100644
index 0000000..4a3e553
--- /dev/null
+++ b/e2e/tests/passkey-full-setup-virtual-auth.spec.ts
@@ -0,0 +1,75 @@
+/**
+ * End-to-end passkey registration with a CDP virtual authenticator (no human).
+ * Runs against the default fixture URL (http://localhost:4444).
+ *
+ * If this fails, the passkey stack (options → create → verify) is broken on localhost.
+ */
+
+import { readFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { expect, test } from "../fixtures";
+import { refreshServerPatAfterDevBypass } from "../fixtures/refresh-server-pat";
+import { addVirtualWebAuthnAuthenticator } from "../fixtures/virtual-authenticator";
+
+const ADMIN_AFTER_SETUP_URL = /\/_emdash\/admin(\/login)?/;
+
+const SERVER_INFO_PATH = join(tmpdir(), "emdash-pw-server.json");
+
+function fixtureBaseUrl(): string {
+	return JSON.parse(readFileSync(SERVER_INFO_PATH, "utf-8")).baseUrl as string;
+}
+
+async function resetSetup(): Promise<void> {
+	const base = fixtureBaseUrl();
+	const res = await fetch(`${base}/_emdash/api/setup/dev-reset`, {
+		method: "POST",
+		headers: { "X-EmDash-Request": "1", Origin: base },
+	});
+	if (!res.ok) throw new Error(`dev-reset failed: ${res.status}`);
+}
+
+async function restoreFixtureSetup(): Promise<void> {
+	await refreshServerPatAfterDevBypass(fixtureBaseUrl());
+}
+
+test.describe("Setup wizard passkey with virtual authenticator (localhost)", () => {
+	test.describe.configure({ mode: "serial" });
+
+	test.beforeEach(async () => {
+		await resetSetup();
+	});
+
+	test.afterAll(async () => {
+		await restoreFixtureSetup();
+	});
+
+	test("completes full setup including passkey registration", async ({ admin, page }) => {
+		test.setTimeout(120_000);
+		const removeAuth = await addVirtualWebAuthnAuthenticator(page);
+
+		try {
+			await admin.goToSetup();
+
+			await page.getByLabel("Site Title").fill("Virtual Auth Site");
+			await page.getByRole("button", { name: "Continue" }).click();
+			await expect(page.locator("text=Create your account")).toBeVisible();
+
+			await page.getByLabel("Your Email").fill("virtual-auth@example.com");
+			await page.getByLabel("Your Name").fill("Virtual Auth User");
+			await page.getByRole("button", { name: "Continue" }).click();
+
+			await expect(page.locator("text=Set up your passkey")).toBeVisible();
+			await page.getByRole("button", { name: "Create Passkey" }).click();
+
+			// admin-verify creates the user but does not set a session; wizard sends user to /_emdash/admin and auth redirects to login.
+			await expect(page).toHaveURL(ADMIN_AFTER_SETUP_URL, { timeout: 60_000 });
+			await expect(page.locator("text=Set up your passkey")).toHaveCount(0);
+			await expect(page.locator("text=Registration was cancelled or timed out")).toHaveCount(0);
+			await expect(page.locator("text=Invalid origin")).toHaveCount(0);
+		} finally {
+			await removeAuth();
+		}
+	});
+});
diff --git a/e2e/tests/setup-wizard.spec.ts b/e2e/tests/setup-wizard.spec.ts
index 4f6188a..e007a8b 100644
--- a/e2e/tests/setup-wizard.spec.ts
+++ b/e2e/tests/setup-wizard.spec.ts
@@ -11,6 +11,7 @@
  */
 
 import { test, expect } from "../fixtures";
+import { refreshServerPatAfterDevBypass } from "../fixtures/refresh-server-pat";
 
 const BASE_URL = "http://localhost:4444";
 const ADMIN_DASHBOARD_PATTERN = /\/_emdash\/admin\/?$/;
@@ -26,10 +27,7 @@ async function resetSetup(): Promise<void> {
 }
 
 async function restoreSetup(): Promise<void> {
-	const res = await fetch(`${BASE_URL}/_emdash/api/setup/dev-bypass?token=1`);
-	if (!res.ok) {
-		throw new Error(`dev-bypass failed (${res.status}): ${await res.text()}`);
-	}
+	await refreshServerPatAfterDevBypass(BASE_URL);
 }
 
 test.describe("Setup Wizard", () => {
diff --git a/packages/admin/src/components/auth/PasskeyLogin.tsx b/packages/admin/src/components/auth/PasskeyLogin.tsx
index 168fc66..a5a5937 100644
--- a/packages/admin/src/components/auth/PasskeyLogin.tsx
+++ b/packages/admin/src/components/auth/PasskeyLogin.tsx
@@ -15,6 +15,10 @@ import { Button, Input } from "@cloudflare/kumo";
 import * as React from "react";
 
 import { apiFetch, parseApiResponse } from "../../lib/api/client";
+import {
+	isPasskeyEnvironmentUsable,
+	isWebAuthnSecureContext,
+} from "../../lib/webauthn-environment";
 
 // ============================================================================
 // Constants
@@ -74,22 +78,11 @@ type LoginState =
 	| { status: "error"; message: string }
 	| { status: "success" };
 
-/**
- * Check if WebAuthn is supported in the current browser
- */
-function isWebAuthnSupported(): boolean {
-	return (
-		typeof window !== "undefined" &&
-		window.PublicKeyCredential !== undefined &&
-		typeof window.PublicKeyCredential === "function"
-	);
-}
-
 /**
  * Check if conditional mediation (autofill) is supported
  */
 async function isConditionalMediationSupported(): Promise<boolean> {
-	if (!isWebAuthnSupported()) return false;
+	if (!isPasskeyEnvironmentUsable()) return false;
 	try {
 		return (await PublicKeyCredential.isConditionalMediationAvailable?.()) ?? false;
 	} catch {
@@ -142,8 +135,11 @@ export function PasskeyLogin({
 	const [email, setEmail] = React.useState("");
 	const [supportsConditional, setSupportsConditional] = React.useState(false);
 
-	// Check WebAuthn support on mount
-	const isSupported = React.useMemo(() => isWebAuthnSupported(), []);
+	const isSupported = React.useMemo(() => isPasskeyEnvironmentUsable(), []);
+	const insecureContext = React.useMemo(
+		() => typeof window !== "undefined" && !isWebAuthnSecureContext(),
+		[],
+	);
 
 	// Check conditional mediation support
 	React.useEffect(() => {
@@ -155,7 +151,9 @@ export function PasskeyLogin({
 			if (!isSupported) {
 				setState({
 					status: "error",
-					message: "WebAuthn is not supported in this browser",
+					message: insecureContext
+						? "Passkeys require HTTPS or http://localhost (with your port); this hostname is not a secure browser context."
+						: "WebAuthn is not supported in this browser",
 				});
 				return;
 			}
@@ -280,17 +278,37 @@ export function PasskeyLogin({
 				onError?.(new Error(userMessage));
 			}
 		},
-		[isSupported, optionsEndpoint, verifyEndpoint, email, supportsConditional, onSuccess, onError],
+		[
+			isSupported,
+			insecureContext,
+			optionsEndpoint,
+			verifyEndpoint,
+			email,
+			supportsConditional,
+			onSuccess,
+			onError,
+		],
 	);
 
-	// Not supported message
 	if (!isSupported) {
 		return (
 			<div className="rounded-lg border border-kumo-danger/50 bg-kumo-danger/10 p-4">
-				<h3 className="font-medium text-kumo-danger">Passkeys Not Supported</h3>
+				<h3 className="font-medium text-kumo-danger">Passkeys Not Available Here</h3>
 				<p className="mt-1 text-sm text-kumo-subtle">
-					Your browser doesn't support passkeys. Please use a modern browser like Chrome, Safari,
-					Firefox, or Edge.
+					{insecureContext ? (
+						<>
+							Passkeys require a <strong className="text-kumo-default">secure context</strong>: use{" "}
+							<strong className="text-kumo-default">HTTPS</strong>, or open the admin at{" "}
+							<strong className="text-kumo-default">http://localhost</strong> (with your dev port).
+							Plain <code className="text-xs">http://</code> on a custom hostname is not treated as
+							secure, even on loopback.
+						</>
+					) : (
+						<>
+							Your browser doesn't support passkeys. Please use a modern browser like Chrome,
+							Safari, Firefox, or Edge.
+						</>
+					)}
 				</p>
 			</div>
 		);
diff --git a/packages/admin/src/components/auth/PasskeyRegistration.tsx b/packages/admin/src/components/auth/PasskeyRegistration.tsx
index e79b525..48cc607 100644
--- a/packages/admin/src/components/auth/PasskeyRegistration.tsx
+++ b/packages/admin/src/components/auth/PasskeyRegistration.tsx
@@ -15,6 +15,10 @@ import { Button, Input } from "@cloudflare/kumo";
 import * as React from "react";
 
 import { apiFetch, parseApiResponse } from "../../lib/api/client";
+import {
+	isPasskeyEnvironmentUsable,
+	isWebAuthnSecureContext,
+} from "../../lib/webauthn-environment";
 
 // ============================================================================
 // Constants
@@ -95,17 +99,6 @@ type RegistrationState =
 	| { status: "error"; message: string }
 	| { status: "success" };
 
-/**
- * Check if WebAuthn is supported in the current browser
- */
-function isWebAuthnSupported(): boolean {
-	return (
-		typeof window !== "undefined" &&
-		window.PublicKeyCredential !== undefined &&
-		typeof window.PublicKeyCredential === "function"
-	);
-}
-
 /**
  * Convert base64url to ArrayBuffer
  */
@@ -153,8 +146,12 @@ export function PasskeyRegistration({
 	});
 	const [passkeyName, setPasskeyName] = React.useState("");
 
-	// Check WebAuthn support on mount
-	const isSupported = React.useMemo(() => isWebAuthnSupported(), []);
+	// Secure context (HTTPS or http://localhost) + PublicKeyCredential
+	const isSupported = React.useMemo(() => isPasskeyEnvironmentUsable(), []);
+	const insecureContext = React.useMemo(
+		() => typeof window !== "undefined" && !isWebAuthnSecureContext(),
+		[],
+	);
 
 	const handleRegister = React.useCallback(async () => {
 		if (!isSupported) {
@@ -292,14 +289,26 @@ export function PasskeyRegistration({
 		onError,
 	]);
 
-	// Not supported message
+	// Not usable (insecure origin vs missing API — browser hides WebAuthn the same way)
 	if (!isSupported) {
 		return (
 			<div className="rounded-lg border border-kumo-danger/50 bg-kumo-danger/10 p-4">
-				<h3 className="font-medium text-kumo-danger">Passkeys Not Supported</h3>
+				<h3 className="font-medium text-kumo-danger">Passkeys Not Available Here</h3>
 				<p className="mt-1 text-sm text-kumo-subtle">
-					Your browser doesn't support passkeys. Please use a modern browser like Chrome, Safari,
-					Firefox, or Edge.
+					{insecureContext ? (
+						<>
+							Passkeys require a <strong className="text-kumo-default">secure context</strong>: use{" "}
+							<strong className="text-kumo-default">HTTPS</strong>, or open the admin at{" "}
+							<strong className="text-kumo-default">http://localhost</strong> (with your dev port).
+							Plain <code className="text-xs">http://</code> on a custom hostname is not treated as
+							secure, even on loopback.
+						</>
+					) : (
+						<>
+							Your browser doesn't support passkeys. Please use a modern browser like Chrome,
+							Safari, Firefox, or Edge.
+						</>
+					)}
 				</p>
 			</div>
 		);
diff --git a/packages/admin/src/lib/webauthn-environment.ts b/packages/admin/src/lib/webauthn-environment.ts
new file mode 100644
index 0000000..60f13f5
--- /dev/null
+++ b/packages/admin/src/lib/webauthn-environment.ts
@@ -0,0 +1,25 @@
+/**
+ * WebAuthn is only available in a browser "secure context": HTTPS, or special-cased
+ * loopback hosts such as `http://localhost` / `http://127.0.0.1`.
+ *
+ * An origin like `http://emdash.local:8081` resolves to 127.0.0.1 but is still
+ * **not** a secure context, so `PublicKeyCredential` is hidden — the same symptom
+ * as an unsupported browser.
+ */
+
+export function isWebAuthnSecureContext(): boolean {
+	return typeof window !== "undefined" && window.isSecureContext;
+}
+
+export function isPublicKeyCredentialConstructorAvailable(): boolean {
+	return (
+		typeof window !== "undefined" &&
+		window.PublicKeyCredential !== undefined &&
+		typeof window.PublicKeyCredential === "function"
+	);
+}
+
+/** True when the page can use `navigator.credentials` for passkeys. */
+export function isPasskeyEnvironmentUsable(): boolean {
+	return isWebAuthnSecureContext() && isPublicKeyCredentialConstructorAvailable();
+}
diff --git a/packages/admin/tests/lib/webauthn-environment.test.ts b/packages/admin/tests/lib/webauthn-environment.test.ts
new file mode 100644
index 0000000..e369e47
--- /dev/null
+++ b/packages/admin/tests/lib/webauthn-environment.test.ts
@@ -0,0 +1,54 @@
+import { describe, it, expect, afterEach } from "vitest";
+
+import {
+	isPasskeyEnvironmentUsable,
+	isPublicKeyCredentialConstructorAvailable,
+	isWebAuthnSecureContext,
+} from "../../src/lib/webauthn-environment";
+
+describe("webauthn-environment", () => {
+	const origPk = globalThis.window.PublicKeyCredential;
+	const desc = Object.getOwnPropertyDescriptor(globalThis.window, "isSecureContext");
+
+	afterEach(() => {
+		if (origPk === undefined) {
+			delete (globalThis.window as { PublicKeyCredential?: unknown }).PublicKeyCredential;
+		} else {
+			Object.defineProperty(globalThis.window, "PublicKeyCredential", {
+				value: origPk,
+				configurable: true,
+				writable: true,
+			});
+		}
+		if (desc) Object.defineProperty(globalThis.window, "isSecureContext", desc);
+	});
+
+	it("is usable only when secure context and PublicKeyCredential constructor exist", () => {
+		Object.defineProperty(globalThis.window, "isSecureContext", {
+			value: true,
+			configurable: true,
+		});
+		Object.defineProperty(globalThis.window, "PublicKeyCredential", {
+			value: function PublicKeyCredential() {},
+			configurable: true,
+			writable: true,
+		});
+		expect(isWebAuthnSecureContext()).toBe(true);
+		expect(isPublicKeyCredentialConstructorAvailable()).toBe(true);
+		expect(isPasskeyEnvironmentUsable()).toBe(true);
+	});
+
+	it("is not usable in an insecure context even if PublicKeyCredential is defined", () => {
+		Object.defineProperty(globalThis.window, "isSecureContext", {
+			value: false,
+			configurable: true,
+		});
+		Object.defineProperty(globalThis.window, "PublicKeyCredential", {
+			value: function PublicKeyCredential() {},
+			configurable: true,
+			writable: true,
+		});
+		expect(isWebAuthnSecureContext()).toBe(false);
+		expect(isPasskeyEnvironmentUsable()).toBe(false);
+	});
+});
diff --git a/packages/core/src/astro/integration/index.ts b/packages/core/src/astro/integration/index.ts
index 14b56d6..3ed69a2 100644
--- a/packages/core/src/astro/integration/index.ts
+++ b/packages/core/src/astro/integration/index.ts
@@ -90,6 +90,22 @@ export function emdash(config: EmDashConfig = {}): AstroIntegration {
 		}
 	}
 
+	if (resolvedConfig.passkeyPublicOrigin) {
+		const raw = resolvedConfig.passkeyPublicOrigin;
+		try {
+			const parsed = new URL(raw);
+			if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
+				throw new Error(`passkeyPublicOrigin must be http or https (got ${parsed.protocol})`);
+			}
+			resolvedConfig.passkeyPublicOrigin = parsed.origin;
+		} catch (e) {
+			if (e instanceof TypeError) {
+				throw new Error(`Invalid passkeyPublicOrigin: "${raw}"`, { cause: e });
+			}
+			throw e;
+		}
+	}
+
 	// Plugin descriptors from config
 	const pluginDescriptors = resolvedConfig.plugins ?? [];
 	const sandboxedDescriptors = resolvedConfig.sandboxed ?? [];
@@ -136,6 +152,7 @@ export function emdash(config: EmDashConfig = {}): AstroIntegration {
 		storage: resolvedConfig.storage,
 		auth: resolvedConfig.auth,
 		marketplace: resolvedConfig.marketplace,
+		passkeyPublicOrigin: resolvedConfig.passkeyPublicOrigin,
 	};
 
 	// Determine auth mode for route injection
diff --git a/packages/core/src/astro/integration/runtime.ts b/packages/core/src/astro/integration/runtime.ts
index 63efaef..7b000d7 100644
--- a/packages/core/src/astro/integration/runtime.ts
+++ b/packages/core/src/astro/integration/runtime.ts
@@ -262,6 +262,19 @@ export interface EmDashConfig {
 	 */
 	marketplace?: string;
 
+	/**
+	 * Public browser origin for passkey verification (rpId + expected WebAuthn origin).
+	 *
+	 * Use when `Astro.url` / `request.url` do not match what users open — common with a
+	 * **TLS-terminating reverse proxy**: the app often sees `http://` on the internal hop
+	 * while the browser uses `https://`, which breaks WebAuthn origin checks.
+	 *
+	 * Set to the full origin users type in the address bar (no path), e.g.
+	 * `https://emdash.local:8443`. Prefer fixing `security.allowedDomains` for the proxy first;
+	 * use this when the reconstructed URL still diverges from the browser.
+	 */
+	passkeyPublicOrigin?: string;
+
 	/**
 	 * Enable playground mode for ephemeral "try EmDash" sites.
 	 *
diff --git a/packages/core/src/astro/routes/api/auth/invite/complete.ts b/packages/core/src/astro/routes/api/auth/invite/complete.ts
index 9a49822..8333afb 100644
--- a/packages/core/src/astro/routes/api/auth/invite/complete.ts
+++ b/packages/core/src/astro/routes/api/auth/invite/complete.ts
@@ -22,6 +22,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals, session }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -37,7 +38,7 @@ export const POST: APIRoute = async ({ request, locals, session }) => {
 		const url = new URL(request.url);
 		const options = new OptionsRepository(emdash.db);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Verify the passkey registration response
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/auth/passkey/options.ts b/packages/core/src/astro/routes/api/auth/passkey/options.ts
index ba8e69f..51fb533 100644
--- a/packages/core/src/astro/routes/api/auth/passkey/options.ts
+++ b/packages/core/src/astro/routes/api/auth/passkey/options.ts
@@ -23,6 +23,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -62,7 +63,7 @@ export const POST: APIRoute = async ({ request, locals }) => {
 		const url = new URL(request.url);
 		const options = new OptionsRepository(emdash.db);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Generate authentication options
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/auth/passkey/register/options.ts b/packages/core/src/astro/routes/api/auth/passkey/register/options.ts
index 38256db..b4b2bef 100644
--- a/packages/core/src/astro/routes/api/auth/passkey/register/options.ts
+++ b/packages/core/src/astro/routes/api/auth/passkey/register/options.ts
@@ -22,6 +22,7 @@ const MAX_PASSKEYS = 10;
 
 export const POST: APIRoute = async ({ request, locals }) => {
 	const { emdash, user } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -52,7 +53,7 @@ export const POST: APIRoute = async ({ request, locals }) => {
 		const url = new URL(request.url);
 		const optionsRepo = new OptionsRepository(emdash.db);
 		const siteName = (await optionsRepo.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Generate registration options
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/auth/passkey/register/verify.ts b/packages/core/src/astro/routes/api/auth/passkey/register/verify.ts
index 8270988..56eb123 100644
--- a/packages/core/src/astro/routes/api/auth/passkey/register/verify.ts
+++ b/packages/core/src/astro/routes/api/auth/passkey/register/verify.ts
@@ -31,6 +31,7 @@ interface PasskeyResponse {
 
 export const POST: APIRoute = async ({ request, locals }) => {
 	const { emdash, user } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -58,7 +59,7 @@ export const POST: APIRoute = async ({ request, locals }) => {
 		const url = new URL(request.url);
 		const optionsRepo = new OptionsRepository(emdash.db);
 		const siteName = (await optionsRepo.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Verify the registration response
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/auth/passkey/verify.ts b/packages/core/src/astro/routes/api/auth/passkey/verify.ts
index f8e0061..f8949bf 100644
--- a/packages/core/src/astro/routes/api/auth/passkey/verify.ts
+++ b/packages/core/src/astro/routes/api/auth/passkey/verify.ts
@@ -20,6 +20,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals, session }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -33,7 +34,7 @@ export const POST: APIRoute = async ({ request, locals, session }) => {
 		const url = new URL(request.url);
 		const options = new OptionsRepository(emdash.db);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Authenticate with passkey
 		const adapter = createKyselyAdapter(emdash.db);
diff --git a/packages/core/src/astro/routes/api/auth/signup/complete.ts b/packages/core/src/astro/routes/api/auth/signup/complete.ts
index 1ebcf5b..1af7d67 100644
--- a/packages/core/src/astro/routes/api/auth/signup/complete.ts
+++ b/packages/core/src/astro/routes/api/auth/signup/complete.ts
@@ -22,6 +22,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals, session }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -37,7 +38,7 @@ export const POST: APIRoute = async ({ request, locals, session }) => {
 		const url = new URL(request.url);
 		const options = new OptionsRepository(emdash.db);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Verify the passkey registration response
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/setup/admin-verify.ts b/packages/core/src/astro/routes/api/setup/admin-verify.ts
index 0162a49..ca9bd74 100644
--- a/packages/core/src/astro/routes/api/setup/admin-verify.ts
+++ b/packages/core/src/astro/routes/api/setup/admin-verify.ts
@@ -21,6 +21,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -57,7 +58,7 @@ export const POST: APIRoute = async ({ request, locals }) => {
 		// Get passkey config
 		const url = new URL(request.url);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Verify the registration response
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/astro/routes/api/setup/admin.ts b/packages/core/src/astro/routes/api/setup/admin.ts
index 90447ea..fe091cb 100644
--- a/packages/core/src/astro/routes/api/setup/admin.ts
+++ b/packages/core/src/astro/routes/api/setup/admin.ts
@@ -20,6 +20,7 @@ import { OptionsRepository } from "#db/repositories/options.js";
 
 export const POST: APIRoute = async ({ request, locals }) => {
 	const { emdash } = locals;
+	const passkeyPublicOrigin = emdash?.config.passkeyPublicOrigin;
 
 	if (!emdash?.db) {
 		return apiError("NOT_CONFIGURED", "EmDash is not initialized", 500);
@@ -56,7 +57,7 @@ export const POST: APIRoute = async ({ request, locals }) => {
 		// Get passkey config
 		const url = new URL(request.url);
 		const siteName = (await options.get<string>("emdash:site_title")) ?? undefined;
-		const passkeyConfig = getPasskeyConfig(url, siteName);
+		const passkeyConfig = getPasskeyConfig(url, siteName, passkeyPublicOrigin);
 
 		// Generate registration options
 		const challengeStore = createChallengeStore(emdash.db);
diff --git a/packages/core/src/auth/passkey-config.ts b/packages/core/src/auth/passkey-config.ts
index 1ece1d0..d373916 100644
--- a/packages/core/src/auth/passkey-config.ts
+++ b/packages/core/src/auth/passkey-config.ts
@@ -15,10 +15,31 @@ export interface PasskeyConfig {
 /**
  * Get passkey configuration from request URL
  *
- * @param url The request URL
- * @param siteName Optional site name for rpName (defaults to hostname)
+ * @param url The request URL (typically `new URL(Astro.request.url)` or `new URL(request.url)`)
+ * @param siteName Optional site name for rpName (defaults to hostname from `url` or public origin)
+ * @param passkeyPublicOrigin Optional browser-facing origin (see `EmDashConfig.passkeyPublicOrigin`).
+ *        When set, **origin** and **rpId** are taken from this URL so they match WebAuthn `clientData.origin`.
+ * @throws If `passkeyPublicOrigin` is non-empty but not parseable by `new URL()`.
  */
-export function getPasskeyConfig(url: URL, siteName?: string): PasskeyConfig {
+export function getPasskeyConfig(
+	url: URL,
+	siteName?: string,
+	passkeyPublicOrigin?: string,
+): PasskeyConfig {
+	if (passkeyPublicOrigin) {
+		let publicUrl: URL;
+		try {
+			publicUrl = new URL(passkeyPublicOrigin);
+		} catch (e) {
+			throw new Error(`Invalid passkeyPublicOrigin: "${passkeyPublicOrigin}"`, { cause: e });
+		}
+		return {
+			rpName: siteName || publicUrl.hostname,
+			rpId: publicUrl.hostname,
+			origin: publicUrl.origin,
+		};
+	}
+
 	return {
 		rpName: siteName || url.hostname,
 		rpId: url.hostname,
diff --git a/packages/core/tests/unit/auth/passkey-config.test.ts b/packages/core/tests/unit/auth/passkey-config.test.ts
index f9d1009..bf942fb 100644
--- a/packages/core/tests/unit/auth/passkey-config.test.ts
+++ b/packages/core/tests/unit/auth/passkey-config.test.ts
@@ -2,8 +2,54 @@ import { describe, it, expect } from "vitest";
 
 import { getPasskeyConfig } from "../../../src/auth/passkey-config.js";
 
+/** URL shape from `new URL(request.url)` after trusted proxy + Astro `security.allowedDomains`. */
+function urlAfterTrustedProxy(path: string, host: string, proto: "http" | "https"): URL {
+	return new URL(path, `${proto}://${host}`);
+}
+
 describe("passkey-config", () => {
+	describe("getPasskeyConfig() via emulated reverse proxy URL", () => {
+		const internalDevUrl = "http://127.0.0.1:4321/_emdash/api/auth/passkey/register/options";
+
+		it("loopback URL alone matches Node before rewrite — rpId is not the public host", () => {
+			const url = new URL(internalDevUrl);
+			expect(getPasskeyConfig(url).rpId).toBe("127.0.0.1");
+		});
+
+		it("forwarded Host/Proto yield the URL handlers see; rp matches HTTP reverse-proxy edge", () => {
+			const url = urlAfterTrustedProxy(
+				"/_emdash/api/auth/passkey/register/options",
+				"emdash.local:8080",
+				"http",
+			);
+			const config = getPasskeyConfig(url, "My Site");
+			expect(config.rpId).toBe("emdash.local");
+			expect(config.rpName).toBe("My Site");
+			expect(config.origin).toBe("http://emdash.local:8080");
+		});
+
+		it("HTTPS listener on proxy with HTTP upstream: passkeyPublicOrigin aligns origin with browser", () => {
+			const urlAstroSeesFromForwardedHttp = urlAfterTrustedProxy(
+				"/_emdash/api/setup/admin",
+				"emdash.local:8080",
+				"http",
+			);
+			const browserOrigin = "https://emdash.local:8443";
+			const config = getPasskeyConfig(urlAstroSeesFromForwardedHttp, "My Site", browserOrigin);
+			expect(config.rpId).toBe("emdash.local");
+			expect(config.rpName).toBe("My Site");
+			expect(config.origin).toBe(browserOrigin);
+		});
+	});
+
 	describe("getPasskeyConfig()", () => {
+		it("throws when passkeyPublicOrigin is not a valid URL", () => {
+			const url = new URL("http://localhost:4321/admin");
+			expect(() => getPasskeyConfig(url, "Site", "::not-a-url")).toThrow(
+				"Invalid passkeyPublicOrigin",
+			);
+		});
+
 		it("extracts rpId from localhost URL", () => {
 			const url = new URL("http://localhost:4321/admin");
 			const config = getPasskeyConfig(url);
@@ -78,5 +124,47 @@ describe("passkey-config", () => {
 			expect(config.origin).toBe("https://example.com");
 			expect(config.rpId).toBe("example.com");
 		});
+
+		it("documents HTTPS reverse-proxy dev pitfall: server URL scheme must match the browser", () => {
+			const serverDevUrl = new URL("http://emdash.local:8443/_emdash/api/setup/admin");
+			const browserPageOrigin = new URL("https://emdash.local:8443/_emdash/admin/setup");
+
+			const fromServer = getPasskeyConfig(serverDevUrl);
+			const fromBrowser = getPasskeyConfig(browserPageOrigin);
+
+			expect(fromServer.rpId).toBe(fromBrowser.rpId);
+			expect(fromServer.origin).toBe("http://emdash.local:8443");
+			expect(fromBrowser.origin).toBe("https://emdash.local:8443");
+			// verifyRegistrationResponse requires clientData.origin === config.origin (see @emdash-cms/auth/passkey)
+			expect(fromServer.origin).not.toBe(fromBrowser.origin);
+		});
+
+		it("passkeyPublicOrigin overrides origin and rpId (TLS termination and loopback request URL)", () => {
+			const fromForwardedHttp = getPasskeyConfig(
+				new URL("http://emdash.local:8443/_emdash/api/setup/admin"),
+				"My Site",
+				"https://emdash.local:8443",
+			);
+			expect(fromForwardedHttp.rpName).toBe("My Site");
+			expect(fromForwardedHttp.rpId).toBe("emdash.local");
+			expect(fromForwardedHttp.origin).toBe("https://emdash.local:8443");
+
+			const fromLoopback = getPasskeyConfig(
+				new URL("http://127.0.0.1:4321/_emdash/api/setup/admin"),
+				"My CMS",
+				"https://public.example:8443",
+			);
+			expect(fromLoopback.rpId).toBe("public.example");
+			expect(fromLoopback.rpName).toBe("My CMS");
+			expect(fromLoopback.origin).toBe("https://public.example:8443");
+
+			const hostnameOnly = getPasskeyConfig(
+				new URL("http://127.0.0.1:4321/x"),
+				undefined,
+				"https://public.example:8443",
+			);
+			expect(hostnameOnly.rpName).toBe("public.example");
+			expect(hostnameOnly.rpId).toBe("public.example");
+		});
 	});
 });
diff --git a/skills/building-emdash-site/references/configuration.md b/skills/building-emdash-site/references/configuration.md
index d24f221..e862806 100644
--- a/skills/building-emdash-site/references/configuration.md
+++ b/skills/building-emdash-site/references/configuration.md
@@ -32,6 +32,10 @@ export default defineConfig({
 });
 ```
 
+### Reverse proxy and passkeys
+
+Passkey `rpId` / `origin` follow Astro `context.url`, which only reflects `X-Forwarded-*` when you declare **allowed public hosts** ([`security.allowedDomains`](https://docs.astro.build/en/reference/configuration-reference/#securityalloweddomains)). In dev, add matching **`vite.server.allowedHosts`** or Vite rejects the proxy `Host`. Use **`emdash({ passkeyPublicOrigin: "https://…" })`** when the browser origin and reconstructed URL still disagree (common with TLS termination). With TLS terminated in front, **`astro dev --host 127.0.0.1`** (loopback) is usually enough: the proxy reaches the dev server locally while **`passkeyPublicOrigin`** matches the browser’s HTTPS origin—without opening the Node port on the LAN.
+
 ### Cloudflare (D1 + R2)
 
 ```javascript