backend barebone done, big chunk of work done

server/internal/auth/password.go

@@ -0,0 +1,103 @@
+// Package auth provides cryptographic core for authentication.
+package auth
+
+import (
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"golang.org/x/crypto/argon2"
+)
+
+// argon2Memory, argon2Time, argon2Threads, argon2KeyLen, and saltLen are parameters
+// recommended by OWASP for Argon2id (memory=65536 KiB, time=3 iterations, parallelism=2).
+const (
+	argon2Memory  = 65536
+	argon2Time    = 3
+	argon2Threads = 2
+	argon2KeyLen  = 32
+	saltLen       = 16
+)
+
+// HashPassword generates an Argon2id hash of the provided password and returns it
+// in PHC string format: $argon2id$v=19$m=...,t=...,p=...$<salt>$<hash>.
+func HashPassword(password string) (string, error) {
+	salt := make([]byte, saltLen)
+	if _, err := rand.Read(salt); err != nil {
+		return "", fmt.Errorf("auth: generate salt: %w", err)
+	}
+	hash := argon2.IDKey([]byte(password), salt, argon2Time, argon2Memory, argon2Threads, argon2KeyLen)
+	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
+	b64Hash := base64.RawStdEncoding.EncodeToString(hash)
+	phc := fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s", argon2.Version, argon2Memory, argon2Time, argon2Threads, b64Salt, b64Hash)
+	return phc, nil
+}
+
+// VerifyPassword checks whether the provided password matches the given Argon2id PHC hash.
+// It returns (true, nil) on match, (false, nil) on mismatch, or (false, error) on invalid format.
+func VerifyPassword(phc, password string) (bool, error) {
+	parts := strings.Split(phc, "$")
+	if len(parts) != 6 || parts[1] != "argon2id" {
+		return false, errors.New("auth: invalid hash format")
+	}
+	// Version
+	vPart := parts[2]
+	if !strings.HasPrefix(vPart, "v=") {
+		return false, errors.New("auth: invalid version format")
+	}
+	v, err := strconv.Atoi(strings.TrimPrefix(vPart, "v="))
+	if err != nil {
+		return false, fmt.Errorf("auth: parse version: %w", err)
+	}
+	if v != argon2.Version {
+		return false, errors.New("auth: incompatible version")
+	}
+	// Parameters
+	mem, t, p := uint32(0), uint32(0), uint32(0)
+	for _, kv := range strings.Split(parts[3], ",") {
+		pair := strings.SplitN(kv, "=", 2)
+		if len(pair) != 2 {
+			return false, errors.New("auth: invalid parameter format")
+		}
+		key, val := pair[0], pair[1]
+		switch key {
+		case "m":
+			x, err := strconv.ParseUint(val, 10, 32)
+			if err != nil {
+				return false, fmt.Errorf("auth: parse memory: %w", err)
+			}
+			mem = uint32(x)
+		case "t":
+			x, err := strconv.ParseUint(val, 10, 32)
+			if err != nil {
+				return false, fmt.Errorf("auth: parse time: %w", err)
+			}
+			t = uint32(x)
+		case "p":
+			x, err := strconv.ParseUint(val, 10, 32)
+			if err != nil {
+				return false, fmt.Errorf("auth: parse threads: %w", err)
+			}
+			p = uint32(x)
+		default:
+			return false, fmt.Errorf("auth: unknown parameter %q", key)
+		}
+	}
+	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
+	if err != nil {
+		return false, fmt.Errorf("auth: decode salt: %w", err)
+	}
+	expected, err := base64.RawStdEncoding.DecodeString(parts[5])
+	if err != nil {
+		return false, fmt.Errorf("auth: decode hash: %w", err)
+	}
+	computed := argon2.IDKey([]byte(password), salt, t, mem, uint8(p), uint32(len(expected)))
+	if subtle.ConstantTimeCompare(computed, expected) == 1 {
+		return true, nil
+	}
+	return false, nil
+}