Update mattermost library (#2152)

* Update mattermost library

* Fix linting

vendor/github.com/hashicorp/go-plugin/mtls.go

@@ -0,0 +1,76 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package plugin
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"math/big"
+	"time"
+)
+
+// generateCert generates a temporary certificate for plugin authentication. The
+// certificate and private key are returns in PEM format.
+func generateCert() (cert []byte, privateKey []byte, err error) {
+	key, err := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
+	sn, err := rand.Int(rand.Reader, serialNumberLimit)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	host := "localhost"
+
+	template := &x509.Certificate{
+		Subject: pkix.Name{
+			CommonName:   host,
+			Organization: []string{"HashiCorp"},
+		},
+		DNSNames: []string{host},
+		ExtKeyUsage: []x509.ExtKeyUsage{
+			x509.ExtKeyUsageClientAuth,
+			x509.ExtKeyUsageServerAuth,
+		},
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageKeyAgreement | x509.KeyUsageCertSign,
+		BasicConstraintsValid: true,
+		SerialNumber:          sn,
+		NotBefore:             time.Now().Add(-30 * time.Second),
+		NotAfter:              time.Now().Add(262980 * time.Hour),
+		IsCA:                  true,
+	}
+
+	der, err := x509.CreateCertificate(rand.Reader, template, template, key.Public(), key)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	var certOut bytes.Buffer
+	if err := pem.Encode(&certOut, &pem.Block{Type: "CERTIFICATE", Bytes: der}); err != nil {
+		return nil, nil, err
+	}
+
+	keyBytes, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	var keyOut bytes.Buffer
+	if err := pem.Encode(&keyOut, &pem.Block{Type: "EC PRIVATE KEY", Bytes: keyBytes}); err != nil {
+		return nil, nil, err
+	}
+
+	cert = certOut.Bytes()
+	privateKey = keyOut.Bytes()
+
+	return cert, privateKey, nil
+}