feat(mfa): passwordless passkey sign-in

server/internal/api/handlers.go

@@ -47,6 +47,8 @@ func RegisterRoutes(r *gin.Engine) {
 	r.POST("/auth/mfa/recovery", auth.HandleMFARecovery)
 	r.POST("/auth/mfa/webauthn/begin", auth.HandleMFAWebAuthnBegin)
 	r.POST("/auth/mfa/webauthn/finish", auth.HandleMFAWebAuthnFinish)
+	r.POST("/auth/passkey/begin", auth.HandlePasskeyLoginBegin)
+	r.POST("/auth/passkey/finish", auth.HandlePasskeyLoginFinish)
 	r.POST("/auth/mfa/enrol/totp/setup", auth.HandleEnrolTOTPSetup)
 	r.POST("/auth/mfa/enrol/totp/confirm", auth.HandleEnrolTOTPConfirm)
 	r.POST("/auth/logout", auth.HandleLogout)

server/internal/auth/passkey_login.go

@@ -0,0 +1,108 @@
+package auth
+
+import (
+	"errors"
+	"net/http"
+
+	"gitea.hostxtra.co.uk/mrhid6/vantage/server/internal/services"
+	"github.com/gin-gonic/gin"
+	"github.com/go-webauthn/webauthn/protocol"
+	"github.com/go-webauthn/webauthn/webauthn"
+)
+
+// HandlePasskeyLoginBegin starts a passwordless sign-in.
+//
+// It repeats every gate /auth/login applies - instance resolution, the locked
+// instance refusal, and the local-login setting - because this is a second
+// front door, and a front door that skips the locks is not a shortcut.
+//
+//	@Summary	Begin passwordless passkey sign-in
+//	@Tags		auth
+//	@Produce	json
+//	@Success	200	{object}	object{publicKey=object,ceremony_id=string}
+//	@Failure	403	{object}	object{error=string}
+//	@Router		/auth/passkey/begin [post]
+func HandlePasskeyLoginBegin(c *gin.Context) {
+	instanceID, err := resolveLoginInstance(c)
+	if errors.Is(err, ErrInstanceLocked) {
+		c.JSON(http.StatusForbidden, gin.H{"error": err.Error(), "locked": true})
+		return
+	}
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+	if !services.LocalLoginPermitted(instanceID) {
+		c.JSON(http.StatusForbidden, gin.H{"error": "password sign-in is disabled for this instance"})
+		return
+	}
+	w, err := webAuthnFor(c)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "could not start sign-in"})
+		return
+	}
+	// Discoverable login: no allowCredentials, so the authenticator offers
+	// whichever resident credential it holds for this RP ID.
+	options, sessionData, err := w.BeginDiscoverableLogin(
+		webauthn.WithUserVerification(protocol.VerificationRequired))
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "could not start sign-in"})
+		return
+	}
+	id, err := saveCeremony(c.Request.Context(), sessionData)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "could not start sign-in"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"publicKey": options.Response, "ceremony_id": id})
+}
+
+// HandlePasskeyLoginFinish verifies a discoverable assertion and mints a
+// session. A user-verified passkey is possession plus a PIN or biometric, so it
+// satisfies require_mfa on its own.
+//
+//	@Summary	Complete passwordless passkey sign-in
+//	@Tags		auth
+//	@Accept		json
+//	@Produce	json
+//	@Param		body	body		object{ceremony_id=string,credential=object}	true	"Assertion"
+//	@Success	200		{object}	object{ok=bool}
+//	@Failure	401		{object}	object{error=string,code=string}
+//	@Router		/auth/passkey/finish [post]
+func HandlePasskeyLoginFinish(c *gin.Context) {
+	instanceID, err := resolveLoginInstance(c)
+	if err != nil {
+		c.JSON(http.StatusForbidden, gin.H{"error": "sign-in is not available here"})
+		return
+	}
+	if !services.LocalLoginPermitted(instanceID) {
+		c.JSON(http.StatusForbidden, gin.H{"error": "password sign-in is disabled for this instance"})
+		return
+	}
+	// finishAssertion is given no userID or email, so it resolves the owning
+	// user itself from the credential ID scoped to this instance - the same
+	// requirement a discoverable login has to meet.
+	cred, err := finishAssertion(c, instanceID, "", "")
+	if err != nil {
+		c.JSON(http.StatusUnauthorized, gin.H{
+			"error": "that passkey could not be verified", "code": "invalid_assertion",
+		})
+		return
+	}
+	stored, err := services.GetPasskeyByCredentialID(instanceID, cred.ID)
+	if err != nil {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
+		return
+	}
+	u, err := services.GetUserInInstance(instanceID, stored.UserID)
+	if err != nil {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
+		return
+	}
+	if err := mintSession(c, u, []string{services.FactorWebAuthn}); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "session save failed"})
+		return
+	}
+	_ = services.TouchPasskey(instanceID, cred.ID, cred.Authenticator.SignCount)
+	c.JSON(http.StatusOK, gin.H{"ok": true})
+}