Add a password policy for distillery users

pkg/password/common.go

@@ -0,0 +1,96 @@
+package password
+
+import (
+	"bufio"
+	"embed"
+	"fmt"
+	"io/fs"
+	"strings"
+)
+
+// CommonPasswordError
+type CommonPasswordError struct {
+	CommonPassword
+}
+
+func (cpe CommonPasswordError) Error() string {
+	return fmt.Sprintf("%q from %q", cpe.Password, cpe.Source)
+}
+
+type CommonPassword struct {
+	Password string
+	Source   string
+}
+
+//go:embed common
+var commonEmbed embed.FS
+
+// CommonPasswords returns a channel that contains all passwords.
+// The caller must drain the channel.
+func CommonPasswords() <-chan CommonPassword {
+	pChan := make(chan CommonPassword, 10)
+	go func() {
+		defer close(pChan)
+
+		fs.WalkDir(commonEmbed, ".", func(path string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+
+			// get the full path
+			if d.IsDir() || !strings.HasSuffix(path, ".txt") {
+				return nil
+			}
+
+			// open it
+			file, err := commonEmbed.Open(path)
+			if err != nil {
+				return err
+			}
+			defer file.Close()
+
+			// scan it line by line
+			scanner := bufio.NewScanner(file)
+			for scanner.Scan() {
+				line := strings.TrimSpace(scanner.Text())
+				if line == "" || strings.HasPrefix(line, "//") {
+					continue
+				}
+				pChan <- CommonPassword{
+					Password: line,
+					Source:   path,
+				}
+			}
+
+			return scanner.Err()
+		})
+	}()
+	return pChan
+}
+
+// CheckCommonPassword checks if a password is a common password.
+//
+// check is called with each candidate password to perform the check.
+// check should return a boolean indicating if the password in question corresponds to the candidate.
+//
+// CheckCommonPassword returns one of three error values.
+//
+// - a CommonPasswordError (when a password matches a common password)
+// - an error returned by check (assuming some check went wrong)
+// - or nil (when a password is not a common password
+func CheckCommonPassword(check func(candidate string) (bool, error)) error {
+	for commmon := range CommonPasswords() {
+		ok, err := check(commmon.Password)
+		if err != nil {
+			return err
+		}
+
+		// password validation passed
+		if ok {
+			return CommonPasswordError{
+				CommonPassword: commmon,
+			}
+		}
+	}
+	return nil
+}