Implement owner setup and browser authentication sessions

internal/adapters/authn/password.go

@@ -0,0 +1,127 @@
+// Package authn implements password hashing and high-entropy credential generation.
+package authn
+
+import (
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"golang.org/x/crypto/argon2"
+)
+
+var ErrInvalidPasswordHash = errors.New("invalid password hash")
+
+type Argon2Parameters struct {
+	MemoryKiB uint32
+	Time      uint32
+	Threads   uint8
+	SaltBytes uint32
+	KeyBytes  uint32
+}
+
+type PasswordHasher struct {
+	parameters Argon2Parameters
+}
+
+func NewPasswordHasher() PasswordHasher {
+	return PasswordHasher{parameters: Argon2Parameters{
+		MemoryKiB: 64 * 1024,
+		Time:      3,
+		Threads:   4,
+		SaltBytes: 16,
+		KeyBytes:  32,
+	}}
+}
+
+func newPasswordHasher(parameters Argon2Parameters) PasswordHasher {
+	return PasswordHasher{parameters: parameters}
+}
+
+func (h PasswordHasher) Hash(password string) (string, error) {
+	salt := make([]byte, h.parameters.SaltBytes)
+	if _, err := rand.Read(salt); err != nil {
+		return "", fmt.Errorf("generate password salt: %w", err)
+	}
+	derived := argon2.IDKey([]byte(password), salt, h.parameters.Time, h.parameters.MemoryKiB, h.parameters.Threads, h.parameters.KeyBytes)
+	return fmt.Sprintf(
+		"$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
+		argon2.Version,
+		h.parameters.MemoryKiB,
+		h.parameters.Time,
+		h.parameters.Threads,
+		base64.RawStdEncoding.EncodeToString(salt),
+		base64.RawStdEncoding.EncodeToString(derived),
+	), nil
+}
+
+func (h PasswordHasher) Verify(password, encoded string) (bool, error) {
+	parameters, salt, expected, err := parsePasswordHash(encoded)
+	if err != nil {
+		return false, err
+	}
+	actual := argon2.IDKey([]byte(password), salt, parameters.Time, parameters.MemoryKiB, parameters.Threads, uint32(len(expected)))
+	return subtle.ConstantTimeCompare(actual, expected) == 1, nil
+}
+
+func parsePasswordHash(encoded string) (Argon2Parameters, []byte, []byte, error) {
+	parts := strings.Split(encoded, "$")
+	if len(parts) != 6 || parts[0] != "" || parts[1] != "argon2id" {
+		return Argon2Parameters{}, nil, nil, ErrInvalidPasswordHash
+	}
+
+	version, err := parseNamedUint(parts[2], "v", 8)
+	if err != nil || version != argon2.Version {
+		return Argon2Parameters{}, nil, nil, ErrInvalidPasswordHash
+	}
+	parameters, err := parseArgon2Parameters(parts[3])
+	if err != nil {
+		return Argon2Parameters{}, nil, nil, err
+	}
+	salt, err := base64.RawStdEncoding.Strict().DecodeString(parts[4])
+	if err != nil || len(salt) < 16 || len(salt) > 64 {
+		return Argon2Parameters{}, nil, nil, ErrInvalidPasswordHash
+	}
+	derived, err := base64.RawStdEncoding.Strict().DecodeString(parts[5])
+	if err != nil || len(derived) < 16 || len(derived) > 64 {
+		return Argon2Parameters{}, nil, nil, ErrInvalidPasswordHash
+	}
+	parameters.SaltBytes = uint32(len(salt))
+	parameters.KeyBytes = uint32(len(derived))
+	return parameters, salt, derived, nil
+}
+
+func parseArgon2Parameters(value string) (Argon2Parameters, error) {
+	parts := strings.Split(value, ",")
+	if len(parts) != 3 {
+		return Argon2Parameters{}, ErrInvalidPasswordHash
+	}
+	memory, err := parseNamedUint(parts[0], "m", 32)
+	if err != nil || memory < 8*1024 || memory > 1024*1024 {
+		return Argon2Parameters{}, ErrInvalidPasswordHash
+	}
+	timeCost, err := parseNamedUint(parts[1], "t", 32)
+	if err != nil || timeCost == 0 || timeCost > 10 {
+		return Argon2Parameters{}, ErrInvalidPasswordHash
+	}
+	threads, err := parseNamedUint(parts[2], "p", 8)
+	if err != nil || threads == 0 || threads > 16 {
+		return Argon2Parameters{}, ErrInvalidPasswordHash
+	}
+	return Argon2Parameters{MemoryKiB: uint32(memory), Time: uint32(timeCost), Threads: uint8(threads)}, nil
+}
+
+func parseNamedUint(value, name string, bitSize int) (uint64, error) {
+	prefix := name + "="
+	if !strings.HasPrefix(value, prefix) {
+		return 0, ErrInvalidPasswordHash
+	}
+	parsed, err := strconv.ParseUint(strings.TrimPrefix(value, prefix), 10, bitSize)
+	if err != nil {
+		return 0, ErrInvalidPasswordHash
+	}
+	return parsed, nil
+}