Send an email if you sign up with an existing email

src/email/email.go

@@ -48,7 +48,47 @@ func SendRegistrationEmail(
 	perf.EndBlock()
 
 	perf.StartBlock("EMAIL", "Sending email")
-	err = sendMail(toAddress, toName, "[handmade.network] Registration confirmation", contents)
+	err = sendMail(toAddress, toName, "[Handmade Network] Registration confirmation", contents)
+	if err != nil {
+		return oops.New(err, "Failed to send email")
+	}
+	perf.EndBlock()
+
+	perf.EndBlock()
+
+	return nil
+}
+
+type ExistingAccountEmailData struct {
+	Name        string
+	Username    string
+	HomepageUrl string
+	LoginUrl    string
+}
+
+func SendExistingAccountEmail(
+	toAddress string,
+	toName string,
+	username string,
+	destination string,
+	perf *perf.RequestPerf,
+) error {
+	perf.StartBlock("EMAIL", "Existing account email")
+
+	perf.StartBlock("EMAIL", "Rendering template")
+	contents, err := renderTemplate("email_account_existing.html", ExistingAccountEmailData{
+		Name:        toName,
+		Username:    username,
+		HomepageUrl: hmnurl.BuildHomepage(),
+		LoginUrl:    hmnurl.BuildLoginPage(destination),
+	})
+	if err != nil {
+		return err
+	}
+	perf.EndBlock()
+
+	perf.StartBlock("EMAIL", "Sending email")
+	err = sendMail(toAddress, toName, "[Handmade Network] You already have an account!", contents)
 	if err != nil {
 		return oops.New(err, "Failed to send email")
 	}
@@ -80,7 +120,7 @@ func SendPasswordReset(toAddress string, toName string, username string, resetTo
 	perf.EndBlock()
 
 	perf.StartBlock("EMAIL", "Sending email")
-	err = sendMail(toAddress, toName, "[handmade.network] Your password reset request", contents)
+	err = sendMail(toAddress, toName, "[Handmade Network] Your password reset request", contents)
 	if err != nil {
 		return oops.New(err, "Failed to send email")
 	}
@@ -118,7 +158,7 @@ func SendTimeMachineEmail(profileUrl, username, userEmail, discordUsername strin
 		return err
 	}
 
-	err = sendMail("team@handmade.network", "HMN Team", "[time machine] New submission", contents)
+	err = sendMail("team@handmade.network", "HMN Team", "[Time Machine] New submission", contents)
 	if err != nil {
 		return oops.New(err, "Failed to send email")
 	}

src/hmnurl/urls.go

@@ -165,7 +165,11 @@ var RegexLoginPage = regexp.MustCompile("^/login$")
 
 func BuildLoginPage(redirectTo string) string {
 	defer CatchPanic()
-	return Url("/login", []Q{{Name: "redirect", Value: redirectTo}})
+	var q []Q
+	if redirectTo != "" {
+		q = append(q, Q{Name: "redirect", Value: redirectTo})
+	}
+	return Url("/login", q)
 }
 
 var RegexLoginWithDiscord = regexp.MustCompile("^/login-with-discord$")

src/templates/src/email_account_existing.html

@@ -0,0 +1,16 @@
+<p>
+    Hello {{ .Name }} - you already have a <a href="{{ .HomepageUrl }}">Handmade Network</a> account. Welcome back!
+</p>
+<p>
+    Your username is <b>{{ .Username }}</b>. To sign in, please visit the following link and try signing in with your existing username:
+</p>
+<p>
+    <a href="{{ .LoginUrl }}">{{ .LoginUrl }}</a>
+</p>
+<p>Thanks,<br />
+The Handmade Network staff.</p>
+
+<hr />
+<p style="font-size:small; -webkit-text-size-adjust:none; color: #666">
+You are receiving this email because someone tried creating a new account with your email address at <a href="{{ .HomepageUrl }}">handmade.network</a>. If that wasn't you, kindly ignore this email.
+</p>

src/templates/src/email_registration.html

@@ -5,7 +5,7 @@
     To complete the registration process, please use the following link:
 </p>
 <p>
-    <a href="{{ .CompleteRegistrationUrl }}">{{ .CompleteRegistrationUrl }}</a>.
+    <a href="{{ .CompleteRegistrationUrl }}">{{ .CompleteRegistrationUrl }}</a>
 </p>
 <p>Thanks,<br />
 The Handmade Network staff.</p>

src/website/auth.go

@@ -232,26 +232,38 @@ func RegisterNewUserSubmit(c *RequestContext) ResponseData {
 		return c.RejectRequest(fmt.Sprintf("Username (%s) already exists.", username))
 	}
 
-	emailAlreadyExists := true
-	_, err = db.QueryOneScalar[int](c, c.Conn,
+	existingUser, err := db.QueryOne[models.User](c, c.Conn,
 		`
-		SELECT id
+		SELECT $columns
 		FROM hmn_user
 		WHERE LOWER(email) = LOWER($1)
 		`,
 		emailAddress,
 	)
-	if err != nil {
-		if errors.Is(err, db.NotFound) {
-			emailAlreadyExists = false
-		} else {
-			return c.ErrorResponse(http.StatusInternalServerError, oops.New(err, "failed to fetch user"))
-		}
+	if errors.Is(err, db.NotFound) {
+		// this is fine
+	} else if err != nil {
+		return c.ErrorResponse(http.StatusInternalServerError, oops.New(err, "failed to fetch user"))
 	}
 	c.Perf.EndBlock()
 
-	if emailAlreadyExists {
-		// NOTE(asaf): Silent rejection so we don't allow attackers to harvest emails.
+	if existingUser != nil {
+		// Render the page as if it was a successful new registration, but
+		// instead send an email to the duplicate email address containing
+		// their actual username. Spammers won't be able to harvest emails, but
+		// normal users will be able to find and access their old accounts.
+
+		err := email.SendExistingAccountEmail(
+			existingUser.Email,
+			existingUser.BestName(),
+			existingUser.Username,
+			destination,
+			c.Perf,
+		)
+		if err != nil {
+			return c.ErrorResponse(http.StatusInternalServerError, oops.New(err, "failed to send existing account email"))
+		}
+
 		return c.Redirect(hmnurl.BuildRegistrationSuccess(), http.StatusSeeOther)
 	}