feat: Token Revocation, Request Object and OP Certification (#130)

FEATURES (and FIXES):
- support OAuth 2.0 Token Revocation [RFC 7009](https://datatracker.ietf.org/doc/html/rfc7009)
- handle request object using `request` parameter [OIDC Core 1.0 Request Object](https://openid.net/specs/openid-connect-core-1_0.html#RequestObject)
- handle response mode
- added some information to the discovery endpoint:
  - revocation_endpoint (added with token revocation) 
  - revocation_endpoint_auth_methods_supported (added with token revocation)
  - revocation_endpoint_auth_signing_alg_values_supported (added with token revocation)
  - token_endpoint_auth_signing_alg_values_supported (was missing)
  - introspection_endpoint_auth_signing_alg_values_supported (was missing)
  - request_object_signing_alg_values_supported (added with request object)
  - request_parameter_supported (added with request object)
 - fixed `removeUserinfoScopes ` now returns the scopes without "userinfo" scopes (profile, email, phone, addedd) [source diff](https://github.com/caos/oidc/pull/130/files#diff-fad50c8c0f065d4dbc49d6c6a38f09c992c8f5d651a479ba00e31b500543559eL170-R171)
- improved error handling (pkg/oidc/error.go) and fixed some wrong OAuth errors (e.g. `invalid_grant` instead of `invalid_request`)
- improved MarshalJSON and added MarshalJSONWithStatus
- removed deprecated PEM decryption from `BytesToPrivateKey`  [source diff](https://github.com/caos/oidc/pull/130/files#diff-fe246e428e399ccff599627c71764de51387b60b4df84c67de3febd0954e859bL11-L19)
- NewAccessTokenVerifier now uses correct (internal) `accessTokenVerifier` [source diff](https://github.com/caos/oidc/pull/130/files#diff-3a01c7500ead8f35448456ef231c7c22f8d291710936cac91de5edeef52ffc72L52-R52)

BREAKING CHANGE:
- move functions from `utils` package into separate packages
- added various methods to the (OP) `Configuration` interface [source diff](https://github.com/caos/oidc/pull/130/files#diff-2538e0dfc772fdc37f057aecd6fcc2943f516c24e8be794cce0e368a26d20a82R19-R32)
- added revocationEndpoint to `WithCustomEndpoints ` [source diff](https://github.com/caos/oidc/pull/130/files#diff-19ae13a743eb7cebbb96492798b1bec556673eb6236b1387e38d722900bae1c3L355-R391)
- remove unnecessary context parameter from JWTProfileExchange [source diff](https://github.com/caos/oidc/pull/130/files#diff-4ed8f6affa4a9631fa8a034b3d5752fbb6a819107141aae00029014e950f7b4cL14)

pkg/http/marshal_test.go

@@ -0,0 +1,156 @@
+package http
+
+import (
+	"bytes"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConcatenateJSON(t *testing.T) {
+	type args struct {
+		first  []byte
+		second []byte
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    []byte
+		wantErr bool
+	}{
+		{
+			"invalid first part, error",
+			args{
+				[]byte(`invalid`),
+				[]byte(`{"some": "thing"}`),
+			},
+			nil,
+			true,
+		},
+		{
+			"invalid second part, error",
+			args{
+				[]byte(`{"some": "thing"}`),
+				[]byte(`invalid`),
+			},
+			nil,
+			true,
+		},
+		{
+			"both valid, merged",
+			args{
+				[]byte(`{"some": "thing"}`),
+				[]byte(`{"another": "thing"}`),
+			},
+
+			[]byte(`{"some": "thing","another": "thing"}`),
+			false,
+		},
+		{
+			"first empty",
+			args{
+				[]byte(`{}`),
+				[]byte(`{"some": "thing"}`),
+			},
+
+			[]byte(`{"some": "thing"}`),
+			false,
+		},
+		{
+			"second empty",
+			args{
+				[]byte(`{"some": "thing"}`),
+				[]byte(`{}`),
+			},
+
+			[]byte(`{"some": "thing"}`),
+			false,
+		},
+		{
+			"both empty",
+			args{
+				[]byte(`{}`),
+				[]byte(`{}`),
+			},
+
+			[]byte(`{}`),
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ConcatenateJSON(tt.args.first, tt.args.second)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ConcatenateJSON() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !bytes.Equal(got, tt.want) {
+				t.Errorf("ConcatenateJSON() got = %v, want %v", string(got), tt.want)
+			}
+		})
+	}
+}
+
+func TestMarshalJSONWithStatus(t *testing.T) {
+	type args struct {
+		i      interface{}
+		status int
+	}
+	type res struct {
+		statusCode int
+		body       string
+	}
+	tests := []struct {
+		name string
+		args args
+		res  res
+	}{
+		{
+			"empty ok",
+			args{
+				nil,
+				200,
+			},
+			res{
+				200,
+				"",
+			},
+		},
+		{
+			"string ok",
+			args{
+				"ok",
+				200,
+			},
+			res{
+				200,
+				`"ok"
+`,
+			},
+		},
+		{
+			"struct ok",
+			args{
+				struct {
+					Test string `json:"test"`
+				}{"ok"},
+				200,
+			},
+			res{
+				200,
+				`{"test":"ok"}
+`,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			MarshalJSONWithStatus(w, tt.args.i, tt.args.status)
+			assert.Equal(t, tt.res.statusCode, w.Result().StatusCode)
+			assert.Equal(t, "application/json", w.Header().Get("content-type"))
+			assert.Equal(t, tt.res.body, w.Body.String())
+		})
+	}
+}