fix: magiclink failing due to passwordStrength check (#1769)

## What kind of change does this PR introduce?

Bug fix

## What is the current behavior?

#1761

## What is the new behavior?

Now the password should generate secure enough with the necessary
password requirements specified in environment variables.

## Additional context

Basically this line in /internal/api/magic_link.go
password.Generate(64, 10, 1, false, true)
Generates an invalid value for this line in /internal/api/signup.go
if err := a.checkPasswordStrength(ctx, p.Password); err != nil {

---------

Co-authored-by: Chris Stockton <180184+cstockton@users.noreply.github.com>

internal/api/magic_link.go

@@ -8,7 +8,7 @@ import (
 	"net/http"
 	"strings"
 
-	"github.com/sethvargo/go-password/password"
+	"github.com/supabase/auth/internal/crypto"
 	"github.com/supabase/auth/internal/models"
 	"github.com/supabase/auth/internal/storage"
 )
@@ -83,7 +83,7 @@ func (a *API) MagicLink(w http.ResponseWriter, r *http.Request) error {
 	if isNewUser {
 		// User either doesn't exist or hasn't completed the signup process.
 		// Sign them up with temporary password.
-		password, err := password.Generate(64, 10, 1, false, true)
+		password, err := crypto.GeneratePassword(config.Password.RequiredCharacters, 33)
 		if err != nil {
 			return internalServerError("error creating user").WithInternalError(err)
 		}

internal/crypto/crypto.go

@@ -51,6 +51,15 @@ func GenerateTokenHash(emailOrPhone, otp string) string {
 	return fmt.Sprintf("%x", sha256.Sum224([]byte(emailOrPhone+otp)))
 }
 
+// Generated a random secure integer from [0, max[
+func secureRandomInt(max int) (int, error) {
+	randomInt, err := rand.Int(rand.Reader, big.NewInt(int64(max)))
+	if err != nil {
+		return 0, errors.WithMessage(err, "Error generating random integer")
+	}
+	return int(randomInt.Int64()), nil
+}
+
 func GenerateSignatures(secrets []string, msgID uuid.UUID, currentTime time.Time, inputPayload []byte) ([]string, error) {
 	SymmetricSignaturePrefix := "v1,"
 	// TODO(joel): Handle asymmetric case once library has been upgraded

internal/crypto/password.go

@@ -234,3 +234,45 @@ func GenerateFromPassword(ctx context.Context, password string) (string, error)
 
 	return string(hash), nil
 }
+
+func GeneratePassword(requiredChars []string, length int) (string, error) {
+	passwordBuilder := strings.Builder{}
+	passwordBuilder.Grow(length)
+
+	// Add required characters
+	for _, group := range requiredChars {
+		if len(group) > 0 {
+			randomIndex, err := secureRandomInt(len(group))
+			if err != nil {
+				return "", err
+			}
+			passwordBuilder.WriteByte(group[randomIndex])
+		}
+	}
+
+	// Define a default character set for random generation (if needed)
+	const allChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+
+	// Fill the rest of the password
+	for passwordBuilder.Len() < length {
+		randomIndex, err := secureRandomInt(len(allChars))
+		if err != nil {
+			return "", err
+		}
+		passwordBuilder.WriteByte(allChars[randomIndex])
+	}
+
+	// Convert to byte slice for shuffling
+	passwordBytes := []byte(passwordBuilder.String())
+
+	// Secure shuffling
+	for i := len(passwordBytes) - 1; i > 0; i-- {
+		j, err := secureRandomInt(i + 1)
+		if err != nil {
+			return "", err
+		}
+		passwordBytes[i], passwordBytes[j] = passwordBytes[j], passwordBytes[i]
+	}
+
+	return string(passwordBytes), nil
+}

internal/crypto/password_test.go

@@ -2,6 +2,7 @@ package crypto
 
 import (
 	"context"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -19,3 +20,67 @@ func TestArgon2(t *testing.T) {
 		assert.NoError(t, CompareHashAndPassword(context.Background(), example, "test"))
 	}
 }
+
+func TestGeneratePassword(t *testing.T) {
+	tests := []struct {
+		name          string
+		requiredChars []string
+		length        int
+		wantErr       bool
+	}{
+		{
+			name:          "Valid password generation",
+			requiredChars: []string{"ABC", "123", "@#$"},
+			length:        12,
+			wantErr:       false,
+		},
+		{
+			name:          "Empty required chars",
+			requiredChars: []string{},
+			length:        8,
+			wantErr:       false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := GeneratePassword(tt.requiredChars, tt.length)
+
+			if (err != nil) != tt.wantErr {
+				t.Errorf("GeneratePassword() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			if len(got) != tt.length {
+				t.Errorf("GeneratePassword() returned password of length %d, want %d", len(got), tt.length)
+			}
+
+			// Check if all required characters are present
+			for _, chars := range tt.requiredChars {
+				found := false
+				for _, c := range got {
+					if strings.ContainsRune(chars, c) {
+						found = true
+						break
+					}
+				}
+				if !found && len(chars) > 0 {
+					t.Errorf("GeneratePassword() missing required character from set %s", chars)
+				}
+			}
+		})
+	}
+
+	// Check for duplicates passwords
+	passwords := make(map[string]bool)
+	for i := 0; i < 30; i++ {
+		p, err := GeneratePassword([]string{"ABC", "123", "@#$"}, 30)
+		if err != nil {
+			t.Errorf("GeneratePassword() unexpected error: %v", err)
+		}
+		if passwords[p] {
+			t.Errorf("GeneratePassword() generated duplicate password: %s", p)
+		}
+		passwords[p] = true
+	}
+}