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/config.go

@@ -2,16 +2,24 @@ package op
 
 import (
 	"errors"
+	"net/http"
 	"net/url"
-	"os"
+	"strings"
 
 	"golang.org/x/text/language"
 )
 
-const OidcDevMode = "CAOS_OIDC_DEV"
+var (
+	ErrInvalidIssuerPath        = errors.New("no fragments or query allowed for issuer")
+	ErrInvalidIssuerNoIssuer    = errors.New("missing issuer")
+	ErrInvalidIssuerURL         = errors.New("invalid url for issuer")
+	ErrInvalidIssuerMissingHost = errors.New("host for issuer missing")
+	ErrInvalidIssuerHTTPS       = errors.New("scheme for issuer must be `https`")
+)
 
 type Configuration interface {
-	Issuer() string
+	IssuerFromRequest(r *http.Request) string
+	Insecure() bool
 	AuthorizationEndpoint() Endpoint
 	TokenEndpoint() Endpoint
 	IntrospectionEndpoint() Endpoint
@@ -37,32 +45,74 @@ type Configuration interface {
 	SupportedUILocales() []language.Tag
 }
 
-func ValidateIssuer(issuer string) error {
+type IssuerFromRequest func(r *http.Request) string
+
+func IssuerFromHost(path string) func(bool) (IssuerFromRequest, error) {
+	return func(allowInsecure bool) (IssuerFromRequest, error) {
+		issuerPath, err := url.Parse(path)
+		if err != nil {
+			return nil, ErrInvalidIssuerURL
+		}
+		if err := ValidateIssuerPath(issuerPath); err != nil {
+			return nil, err
+		}
+		return func(r *http.Request) string {
+			return dynamicIssuer(r.Host, path, allowInsecure)
+		}, nil
+	}
+}
+
+func StaticIssuer(issuer string) func(bool) (IssuerFromRequest, error) {
+	return func(allowInsecure bool) (IssuerFromRequest, error) {
+		if err := ValidateIssuer(issuer, allowInsecure); err != nil {
+			return nil, err
+		}
+		return func(_ *http.Request) string {
+			return issuer
+		}, nil
+	}
+}
+
+func ValidateIssuer(issuer string, allowInsecure bool) error {
 	if issuer == "" {
-		return errors.New("missing issuer")
+		return ErrInvalidIssuerNoIssuer
 	}
 	u, err := url.Parse(issuer)
 	if err != nil {
-		return errors.New("invalid url for issuer")
+		return ErrInvalidIssuerURL
 	}
 	if u.Host == "" {
-		return errors.New("host for issuer missing")
+		return ErrInvalidIssuerMissingHost
 	}
 	if u.Scheme != "https" {
-		if !devLocalAllowed(u) {
-			return errors.New("scheme for issuer must be `https`")
+		if !devLocalAllowed(u, allowInsecure) {
+			return ErrInvalidIssuerHTTPS
 		}
 	}
-	if u.Fragment != "" || len(u.Query()) > 0 {
-		return errors.New("no fragments or query allowed for issuer")
+	return ValidateIssuerPath(u)
+}
+
+func ValidateIssuerPath(issuer *url.URL) error {
+	if issuer.Fragment != "" || len(issuer.Query()) > 0 {
+		return ErrInvalidIssuerPath
 	}
 	return nil
 }
 
-func devLocalAllowed(url *url.URL) bool {
-	_, b := os.LookupEnv(OidcDevMode)
-	if !b {
-		return b
+func devLocalAllowed(url *url.URL, allowInsecure bool) bool {
+	if !allowInsecure {
+		return false
 	}
 	return url.Scheme == "http"
 }
+
+func dynamicIssuer(issuer, path string, allowInsecure bool) string {
+	schema := "https"
+	if allowInsecure {
+		schema = "http"
+	}
+	if len(path) > 0 && !strings.HasPrefix(path, "/") {
+		path = "/" + path
+	}
+	return schema + "://" + issuer + path
+}