[docs] Passkeys (#2105)

docs/docs/.vitepress/sidebar.ts

@@ -44,6 +44,10 @@ export const sidebar = [
                         link: "/photos/features/location-tags",
                     },
                     { text: "Map", link: "/photos/features/map" },
+                    {
+                        text: "Passkeys",
+                        link: "/photos/features/passkeys",
+                    },
                     {
                         text: "Public link",
                         link: "/photos/features/public-link",

docs/docs/photos/features/passkeys.md

@@ -0,0 +1,62 @@
+---
+title: Passkeys
+description: Using passkeys as a second factor for your Ente account
+---
+
+# Passkeys
+
+> [!CAUTION]
+>
+> This is preview documentation for an upcoming feature. This feature has not
+> yet been released yet, so the steps below will not work currently.
+
+Passkeys are a new authentication mechanism that uses strong cryptography built
+into devices, like Windows Hello or Apple's Touch ID. **You can use passkeys as
+a second factor to secure your Ente account.**
+
+> [!TIP]
+>
+> Passkeys are the colloquial term for a WebAuthn (Web Authentication)
+> credentials. To know more technical details about how our passkey verification
+> works, you can see this
+> [technical note in our source code](https://github.com/ente-io/ente/blob/main/web/docs/webauthn-passkeys.md).
+
+## Passkeys and TOTP
+
+Ente already supports TOTP codes (in fact, we built an
+[entire app](https://ente.io/auth/) to store them...). Passkeys serve as an
+alternative 2FA (second factor) mechanism.
+
+If you add a passkey to your Ente account, it will be used instead of any
+existing 2FA codes that you have configured (if any).
+
+## Enabling and disabling passkeys
+
+Passkeys get enabled if you add one (or more) passkeys to your account.
+Conversely, passkeys get disabled if you remove all your existing passkeys.
+
+To add and remove passkeys, use the _Passkey_ option in the settings menu. This
+will open up _accounts.ente.io_, where you can manage your passkeys.
+
+## Login with passkeys
+
+If passkeys are enabled, then _accounts.ente.io_ will automatically open when
+you log into your Ente account on a new device. Here you can follow the
+instructions given by the browser to verify your passkey.
+
+> These instructions different for each browser and device, but generally they
+> will ask you to use the same mechanism that you used when you created the
+> passkey to verify it (scanning a QR code, using your fingerprint, pressing the
+> key on your Yubikey or other security key hardware etc).
+
+## Recovery
+
+If you are unable to login with your passkey (e.g. if you have misplaced the
+hardware key that you used to store your passkey), then you can **recover your
+account by using your Ente recovery key**.
+
+During login, press cancel on the browser dialog to verify your passkey, and
+then select the "Recover two-factor" option in the error message that gets
+shown. This will take you to a place where you can enter your Ente recovery key
+and login into your account. Now you can go to the _Passkey_ page to delete the
+lost passkey and/or add a new one.