Provide the ability to set password hash algorithm parameters (#22942)

This PR refactors and improves the password hashing code within gitea
and makes it possible for server administrators to set the password
hashing parameters

In addition it takes the opportunity to adjust the settings for `pbkdf2`
in order to make the hashing a little stronger.

The majority of this work was inspired by PR #14751 and I would like to
thank @boppy for their work on this.

Thanks to @gusted for the suggestion to adjust the `pbkdf2` hashing
parameters.

Close #14751

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/auth/password/hash/argon2.go

@@ -0,0 +1,80 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"encoding/hex"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"golang.org/x/crypto/argon2"
+)
+
+func init() {
+	Register("argon2", NewArgon2Hasher)
+}
+
+// Argon2Hasher implements PasswordHasher
+// and uses the Argon2 key derivation function, hybrant variant
+type Argon2Hasher struct {
+	time    uint32
+	memory  uint32
+	threads uint8
+	keyLen  uint32
+}
+
+// HashWithSaltBytes a provided password and salt
+func (hasher *Argon2Hasher) HashWithSaltBytes(password string, salt []byte) string {
+	if hasher == nil {
+		return ""
+	}
+	return hex.EncodeToString(argon2.IDKey([]byte(password), salt, hasher.time, hasher.memory, hasher.threads, hasher.keyLen))
+}
+
+// NewArgon2Hasher is a factory method to create an Argon2Hasher
+// The provided config should be either empty or of the form:
+// "<time>$<memory>$<threads>$<keyLen>", where <x> is the string representation
+// of an integer
+func NewArgon2Hasher(config string) *Argon2Hasher {
+	// This default configuration uses the following parameters:
+	// time=2, memory=64*1024, threads=8, keyLen=50.
+	// It will make two passes through the memory, using 64MiB in total.
+	// This matches the original configuration for `argon2` prior to storing hash parameters
+	// in the database.
+	// THESE VALUES MUST NOT BE CHANGED OR BACKWARDS COMPATIBILITY WILL BREAK
+	hasher := &Argon2Hasher{
+		time:    2,
+		memory:  1 << 16,
+		threads: 8,
+		keyLen:  50,
+	}
+
+	if config == "" {
+		return hasher
+	}
+
+	vals := strings.SplitN(config, "$", 4)
+	if len(vals) != 4 {
+		log.Error("invalid argon2 hash spec %s", config)
+		return nil
+	}
+
+	parsed, err := parseUIntParam(vals[0], "time", "argon2", config, nil)
+	hasher.time = uint32(parsed)
+
+	parsed, err = parseUIntParam(vals[1], "memory", "argon2", config, err)
+	hasher.memory = uint32(parsed)
+
+	parsed, err = parseUIntParam(vals[2], "threads", "argon2", config, err)
+	hasher.threads = uint8(parsed)
+
+	parsed, err = parseUIntParam(vals[3], "keyLen", "argon2", config, err)
+	hasher.keyLen = uint32(parsed)
+	if err != nil {
+		return nil
+	}
+
+	return hasher
+}