feat(op): dynamic issuer depending on request / host

BREAKING CHANGE: The OpenID Provider package is now able to handle multiple issuers with a single storage implementation. The issuer will be selected from the host of the request and passed into the context, where every function can read it from if necessary. This results in some fundamental changes:
 - `Configuration` interface:
   - `Issuer() string` has been changed to `IssuerFromRequest(r *http.Request) string`
   - `Insecure() bool` has been added
 - OpenIDProvider interface and dependants:
   - `Issuer` has been removed from Config struct
   - `NewOpenIDProvider` now takes an additional parameter `issuer` and returns a pointer to the public/default implementation and not an OpenIDProvider interface:
     `NewOpenIDProvider(ctx context.Context, config *Config, storage Storage, opOpts ...Option) (OpenIDProvider, error)` changed to `NewOpenIDProvider(ctx context.Context, issuer string, config *Config, storage Storage, opOpts ...Option) (*Provider, error)`
   - therefore the parameter type Option changed to the public type as well: `Option func(o *Provider) error`
   - `AuthCallbackURL(o OpenIDProvider) func(string) string` has been changed to `AuthCallbackURL(o OpenIDProvider) func(context.Context, string) string`
   - `IDTokenHintVerifier() IDTokenHintVerifier` (Authorizer, OpenIDProvider, SessionEnder interfaces), `AccessTokenVerifier() AccessTokenVerifier` (Introspector, OpenIDProvider, Revoker, UserinfoProvider interfaces) and `JWTProfileVerifier() JWTProfileVerifier` (IntrospectorJWTProfile, JWTAuthorizationGrantExchanger, OpenIDProvider, RevokerJWTProfile interfaces) now take a context.Context parameter `IDTokenHintVerifier(context.Context) IDTokenHintVerifier`, `AccessTokenVerifier(context.Context) AccessTokenVerifier` and `JWTProfileVerifier(context.Context) JWTProfileVerifier`
   - `OidcDevMode` (CAOS_OIDC_DEV) environment variable check has been removed, use `WithAllowInsecure()` Option
 - Signing: the signer is not kept in memory anymore, but created on request from the loaded key:
   - `Signer` interface and func `NewSigner` have been removed
   - `ReadySigner(s Signer) ProbesFn` has been removed
   - `CreateDiscoveryConfig(c Configuration, s Signer) *oidc.DiscoveryConfiguration` has been changed to `CreateDiscoveryConfig(r *http.Request, config Configuration, storage DiscoverStorage) *oidc.DiscoveryConfiguration`
   - `Storage` interface:
     - `GetSigningKey(context.Context, chan<- jose.SigningKey)` has been changed to `SigningKey(context.Context) (SigningKey, error)`
     - `KeySet(context.Context) ([]Key, error)` has been added
     - `GetKeySet(context.Context) (*jose.JSONWebKeySet, error)` has been changed to `KeySet(context.Context) ([]Key, error)`
   - `SigAlgorithms(s Signer) []string` has been changed to `SigAlgorithms(ctx context.Context, storage DiscoverStorage) []string`
   - KeyProvider interface: `GetKeySet(context.Context) (*jose.JSONWebKeySet, error)` has been changed to `KeySet(context.Context) ([]Key, error)`
   - `CreateIDToken`: the Signer parameter has been removed

pkg/op/context_test.go

@@ -0,0 +1,76 @@
+package op
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIssuerInterceptor(t *testing.T) {
+	type fields struct {
+		issuerFromRequest IssuerFromRequest
+	}
+	type args struct {
+		r    *http.Request
+		next http.Handler
+	}
+	type res struct {
+		issuer string
+	}
+	tests := []struct {
+		name   string
+		fields fields
+		args   args
+		res    res
+	}{
+		{
+			"empty",
+			fields{
+				func(r *http.Request) string {
+					return ""
+				},
+			},
+			args{},
+			res{
+				issuer: "",
+			},
+		},
+		{
+			"static",
+			fields{
+				func(r *http.Request) string {
+					return "static"
+				},
+			},
+			args{},
+			res{
+				issuer: "static",
+			},
+		},
+		{
+			"host",
+			fields{
+				func(r *http.Request) string {
+					return r.Host
+				},
+			},
+			args{},
+			res{
+				issuer: "issuer.com",
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			i := NewIssuerInterceptor(tt.fields.issuerFromRequest)
+			next := http.HandlerFunc(func(_ http.ResponseWriter, r *http.Request) {
+				assert.Equal(t, tt.res.issuer, IssuerFromContext(r.Context()))
+			})
+			req := httptest.NewRequest("", "https://issuer.com", nil)
+			i.Handler(next).ServeHTTP(nil, req)
+			i.HandlerFunc(next).ServeHTTP(nil, req)
+		})
+	}
+}