Use asym key to sign webhooks (#916)

* use async key pair for webhooks

* fix tests

* fix linter

* improve code

* add key pair to database

* undo some changes

* more undo

* improve docs

* add api-endpoint

* add signaturne api endpoint

* fix error

* fix linting and test

* fix lint

* add test

* migration 006

* no need for migration

* replace httsign lib

* fix lint

Co-authored-by: 6543 <6543@obermui.de>

vendor/github.com/go-ap/httpsig/httpsig.go

@@ -0,0 +1,44 @@
+// Copyright (C) 2017 Space Monkey, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package httpsig
+
+// Algorithm provides methods used to sign/verify signatures.
+type Algorithm interface {
+	Name() string
+	Sign(key interface{}, data []byte) (sig []byte, err error)
+	Verify(key interface{}, data, sig []byte) error
+}
+
+// KeyGetter is an interface used by the verifier to retrieve a key stored
+// by key id.
+//
+// The following types are supported for the specified algorithms:
+// []byte            - HMAC signatures
+// *rsa.PublicKey    - RSA signatures
+// *rsa.PrivateKey   - RSA signatures
+//
+// Other types will treated as if no key was returned.
+type KeyGetter interface {
+	GetKey(id string) (interface{}, error)
+}
+
+// KeyGetterFunc is a convenience type for implementing a KeyGetter with a
+// regular function
+type KeyGetterFunc func(id string) (interface{}, error)
+
+// GetKey calls fn(id)
+func (fn KeyGetterFunc) GetKey(id string) (interface{}, error) {
+	return fn(id)
+}