MVP, no mod tools or anything but it works

vendor/gopkg.in/hlandau/passlib.v1/hash/bcryptsha256/bcryptsha256.go

@@ -0,0 +1,96 @@
+// Package bcryptsha256 implements bcrypt with a SHA256 prehash in a format that is compatible with Python passlib's equivalent bcrypt-sha256 scheme.
+//
+// This is preferred over bcrypt because the prehash essentially renders bcrypt's password length
+// limitation irrelevant; although of course it is less compatible.
+package bcryptsha256
+
+import "gopkg.in/hlandau/passlib.v1/abstract"
+import "gopkg.in/hlandau/passlib.v1/hash/bcrypt"
+import "encoding/base64"
+import "crypto/sha256"
+import "strings"
+import "fmt"
+
+type scheme struct {
+	underlying abstract.Scheme
+	cost       int
+}
+
+// An implementation of Scheme implementing Python passlib's `$bcrypt-sha256$`
+// bcrypt variant. This is bcrypt with a SHA256 prehash, which removes bcrypt's
+// password length limitation.
+var Crypter abstract.Scheme
+
+// The recommended cost for bcrypt-sha256. This may change with subsequent releases.
+const RecommendedCost = bcrypt.RecommendedCost
+
+func init() {
+	Crypter = New(bcrypt.RecommendedCost)
+}
+
+// Instantiates a new Scheme implementing bcrypt with the given cost.
+//
+// The recommended cost is RecommendedCost.
+func New(cost int) abstract.Scheme {
+	return &scheme{
+		underlying: bcrypt.New(cost),
+		cost:       cost,
+	}
+}
+
+func (s *scheme) Hash(password string) (string, error) {
+	p := s.prehash(password)
+	h, err := s.underlying.Hash(p)
+	if err != nil {
+		return "", err
+	}
+
+	return mangle(h), nil
+}
+
+func (s *scheme) Verify(password, hash string) error {
+	p := s.prehash(password)
+	return s.underlying.Verify(p, demangle(hash))
+}
+
+func (s *scheme) prehash(password string) string {
+	h := sha256.New()
+	h.Write([]byte(password))
+	v := base64.StdEncoding.EncodeToString(h.Sum(nil))
+	return v
+}
+
+func (s *scheme) SupportsStub(stub string) bool {
+	return strings.HasPrefix(stub, "$bcrypt-sha256$") && s.underlying.SupportsStub(demangle(stub))
+}
+
+func (s *scheme) NeedsUpdate(stub string) bool {
+	return s.underlying.NeedsUpdate(demangle(stub))
+}
+
+func (s *scheme) String() string {
+	return fmt.Sprintf("bcrypt-sha256(%d)", s.cost)
+}
+
+func demangle(stub string) string {
+	if strings.HasPrefix(stub, "$bcrypt-sha256$2") {
+		parts := strings.Split(stub[15:], "$")
+		// 0: 2a,12
+		// 1: salt
+		// 2: hash
+		parts0 := strings.Split(parts[0], ",")
+		return "$" + parts0[0] + "$" + fmt.Sprintf("%02s", parts0[1]) + "$" + parts[1] + parts[2]
+	} else {
+		return stub
+	}
+}
+
+func mangle(hash string) string {
+	parts := strings.Split(hash[1:], "$")
+	// 0: 2a
+	// 1: rounds
+	// 2: salt + hash
+	salt := parts[2][0:22]
+	h := parts[2][22:]
+	return "$bcrypt-sha256$" + parts[0] + "," + parts[1] + "$" + salt + "$" + h
+}