MVP, no mod tools or anything but it works

vendor/gopkg.in/hlandau/passlib.v1/abstract/compare.go

@@ -0,0 +1,11 @@
+package abstract
+
+import "crypto/subtle"
+
+// Compares two strings (typicaly password hashes) in a secure, constant-time
+// fashion. Returns true iff they are equal.
+func SecureCompare(a, b string) bool {
+	ab := []byte(a)
+	bb := []byte(b)
+	return subtle.ConstantTimeCompare(ab, bb) == 1
+}

vendor/gopkg.in/hlandau/passlib.v1/abstract/errors.go

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+// Package abstract contains the abstract description of the Scheme interface,
+// plus supporting error definitions.
+package abstract
+
+import "fmt"
+
+// Indicates that password verification failed because the provided password
+// does not match the provided hash.
+var ErrInvalidPassword = fmt.Errorf("invalid password")
+
+// Indicates that password verification is not possible because the hashing
+// scheme used by the hash provided is not supported.
+var ErrUnsupportedScheme = fmt.Errorf("unsupported scheme")
+
+// © 2014 Hugo Landau <hlandau@devever.net>  MIT License

vendor/gopkg.in/hlandau/passlib.v1/abstract/scheme.go

@@ -0,0 +1,34 @@
+package abstract
+
+// The Scheme interface provides an abstract interface to an implementation
+// of a particular password hashing scheme. The Scheme generates password
+// hashes from passwords, verifies passwords using password hashes, randomly
+// generates new stubs and can determines whether it recognises a given
+// stub or hash. It may also decide to issue upgrades.
+type Scheme interface {
+	// Hashes a plaintext UTF-8 password using a modular crypt stub. Returns the
+	// hashed password in modular crypt format.
+	//
+	// A modular crypt stub is a prefix of a hash in modular crypt format which
+	// expresses all necessary configuration information, such as salt and
+	// iteration count. For example, for sha256-crypt, a valid stub would be:
+	//
+	//     $5$rounds=6000$salt
+	//
+	// A full modular crypt hash may also be passed as the stub, in which case
+	// the hash is ignored.
+	Hash(password string) (string, error)
+
+	// Verifies a plaintext UTF-8 password using a modular crypt hash.  Returns
+	// an error if the inputs are malformed or the password does not match.
+	Verify(password, hash string) (err error)
+
+	// Returns true iff this crypter supports the given stub.
+	SupportsStub(stub string) bool
+
+	// Returns true iff this stub needs an update.
+	NeedsUpdate(stub string) bool
+
+	// Make a stub with the configured defaults. The salt is generated randomly.
+	//MakeStub() (string, error)
+}