refactor: use struct types for claim related types (#283)

* oidc: add regression tests for token claim json

this helps to verify that the same JSON is produced,
after these types are refactored.

* refactor: use struct types for claim related types

BREAKING CHANGE:
The following types are changed from interface to struct type:

- AccessTokenClaims
- IDTokenClaims
- IntrospectionResponse
- UserInfo and related types.

The following methods of OPStorage now take a pointer to a struct type,
instead of an interface:

- SetUserinfoFromScopes
- SetUserinfoFromToken
- SetIntrospectionFromToken

The following functions are now generic, so that type-safe extension
of Claims is now possible:

- op.VerifyIDTokenHint
- op.VerifyAccessToken
- rp.VerifyTokens
- rp.VerifyIDToken

- Changed UserInfoAddress to pointer in UserInfo and
IntrospectionResponse.
This was needed to make omitempty work correctly.
- Copy or merge maps in IntrospectionResponse and SetUserInfo

* op: add example for VerifyAccessToken

* fix: rp: wrong assignment in WithIssuedAtMaxAge

WithIssuedAtMaxAge assigned its value to v.maxAge, which was wrong.
This change fixes that by assiging the duration to v.maxAgeIAT.

* rp: add VerifyTokens example

* oidc: add standard references to:

- IDTokenClaims
- IntrospectionResponse
- UserInfo

* only count coverage for `./pkg/...`

pkg/oidc/regression_test.go

@@ -0,0 +1,40 @@
+package oidc
+
+// This file contains common functions and data for regression testing
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"path"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+const dataDir = "regression_data"
+
+// jsonFilename builds a filename for the regression testdata.
+// dataDir/<type_name>.json
+func jsonFilename(obj interface{}) string {
+	name := fmt.Sprintf("%T.json", obj)
+	return path.Join(
+		dataDir,
+		strings.TrimPrefix(name, "*"),
+	)
+}
+
+func encodeJSON(t *testing.T, w io.Writer, obj interface{}) {
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "\t")
+	require.NoError(t, enc.Encode(obj))
+}
+
+var regressionData = []interface{}{
+	accessTokenData,
+	idTokenData,
+	introspectionResponseData,
+	userInfoData,
+	jwtProfileAssertionData,
+}