api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/owner_confirm_hex.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+)
+
+func ownerConfirmHex(confirmHex string) error {
+	if confirmHex == "" {
+		return errorMissingField
+	}
+
+	statement := `
+		UPDATE owners
+		SET confirmedEmail=true
+		WHERE ownerHex IN (
+			SELECT ownerHex FROM ownerConfirmHexes
+			WHERE confirmHex=$1
+		);
+	`
+	res, err := db.Exec(statement, confirmHex)
+	if err != nil {
+		logger.Errorf("cannot mark user's confirmedEmail as true: %v\n", err)
+		return errorInternal
+	}
+
+	count, err := res.RowsAffected()
+	if err != nil {
+		logger.Errorf("cannot count rows affected: %v\n", err)
+		return errorInternal
+	}
+
+	if count == 0 {
+		return errorNoSuchConfirmationToken
+	}
+
+	statement = `
+		DELETE FROM ownerConfirmHexes
+		WHERE confirmHex=$1;
+	`
+	_, err = db.Exec(statement, confirmHex)
+	if err != nil {
+		logger.Warningf("cannot remove confirmation token: %v\n", err)
+		// Don't return an error because this is not critical.
+	}
+
+	return nil
+}
+
+func ownerConfirmHexHandler(w http.ResponseWriter, r *http.Request) {
+	if confirmHex := r.FormValue("confirmHex"); confirmHex != "" {
+		if err := ownerConfirmHex(confirmHex); err == nil {
+			http.Redirect(w, r, fmt.Sprintf("%s/login?confirmed=true", os.Getenv("FRONTEND")), http.StatusTemporaryRedirect)
+			return
+		}
+	}
+
+	// TODO: include error message in the URL
+	http.Redirect(w, r, fmt.Sprintf("%s/login?confirmed=false", os.Getenv("FRONTEND")), http.StatusTemporaryRedirect)
+}