Repository: zitadel/oidc (go)

Issue:
Allow custom forwarded header
We have issues at zitadel to use the Forwarded header in production, because our hoster Vercel corrupts the header on the outgoing proxies request.

As a workaround we want to support also x-zitadel-forwarded in the same format as the current forwarded header.

Pull request description:
feat(op): issuer from custom headers
This change allows getting the issuer host from custom headers in the same format the the `Forwarded` header.

Closes #477

### Definition of Ready

- [x] I am happy with the code
- [x] Short description of the feature/issue is added in the pr description
- [x] PR is linked to the corresponding user story
- [x] Acceptance criteria are met
- [x] All open todos and follow ups are defined in a new ticket and justified
- [x] Deviations from the acceptance criteria and design are agreed with the PO and documented.
- [x] No debug or dead code
- [x] My code has no repetitions
- [x] Critical parts are tested automatically
- [x] Where possible E2E tests are implemented
- [x] Documentation/examples are up-to-date
- [x] All non-functional requirements are met
- [ ] Functionality of the acceptance criteria is checked manually on the dev system.



Patch:
diff --git a/pkg/op/config.go b/pkg/op/config.go
index c383480..9fec7cc 100644
--- a/pkg/op/config.go
+++ b/pkg/op/config.go
@@ -54,7 +54,24 @@ type Configuration interface {
 type IssuerFromRequest func(r *http.Request) string
 
 func IssuerFromHost(path string) func(bool) (IssuerFromRequest, error) {
-	return issuerFromForwardedOrHost(path, false)
+	return issuerFromForwardedOrHost(path, new(issuerConfig))
+}
+
+type IssuerFromOption func(c *issuerConfig)
+
+// WithIssuerFromCustomHeaders can be used to customize the header names used.
+// The same rules apply where the first successful host is returned.
+func WithIssuerFromCustomHeaders(headers ...string) IssuerFromOption {
+	return func(c *issuerConfig) {
+		for i, h := range headers {
+			headers[i] = http.CanonicalHeaderKey(h)
+		}
+		c.headers = headers
+	}
+}
+
+type issuerConfig struct {
+	headers []string
 }
 
 // IssuerFromForwardedOrHost tries to establish the Issuer based
@@ -64,11 +81,18 @@ func IssuerFromHost(path string) func(bool) (IssuerFromRequest, error) {
 // If the Forwarded header is not present, no host field is found,
 // or there is a parser error the Request Host will be used as a fallback.
 // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Forwarded
-func IssuerFromForwardedOrHost(path string) func(bool) (IssuerFromRequest, error) {
-	return issuerFromForwardedOrHost(path, true)
+func IssuerFromForwardedOrHost(path string, opts ...IssuerFromOption) func(bool) (IssuerFromRequest, error) {
+	c := &issuerConfig{
+		headers: []string{http.CanonicalHeaderKey("forwarded")},
+	}
+	for _, opt := range opts {
+		opt(c)
+	}
+
+	return issuerFromForwardedOrHost(path, c)
 }
 
-func issuerFromForwardedOrHost(path string, parseForwarded bool) func(bool) (IssuerFromRequest, error) {
+func issuerFromForwardedOrHost(path string, c *issuerConfig) func(bool) (IssuerFromRequest, error) {
 	return func(allowInsecure bool) (IssuerFromRequest, error) {
 		issuerPath, err := url.Parse(path)
 		if err != nil {
@@ -78,26 +102,26 @@ func issuerFromForwardedOrHost(path string, parseForwarded bool) func(bool) (Iss
 			return nil, err
 		}
 		return func(r *http.Request) string {
-			if parseForwarded {
-				if host, ok := hostFromForwarded(r); ok {
-					return dynamicIssuer(host, path, allowInsecure)
-				}
+			if host, ok := hostFromForwarded(r, c.headers); ok {
+				return dynamicIssuer(host, path, allowInsecure)
 			}
 			return dynamicIssuer(r.Host, path, allowInsecure)
 		}, nil
 	}
 }
 
-func hostFromForwarded(r *http.Request) (host string, ok bool) {
-	fwd, err := httpforwarded.ParseFromRequest(r)
-	if err != nil {
-		log.Printf("Err: issuer from forwarded header: %v", err) // TODO change to slog on next branch
-		return "", false
-	}
-	if fwd == nil || len(fwd["host"]) == 0 {
-		return "", false
+func hostFromForwarded(r *http.Request, headers []string) (host string, ok bool) {
+	for _, header := range headers {
+		hosts, err := httpforwarded.ParseParameter("host", r.Header[header])
+		if err != nil {
+			log.Printf("Err: issuer from forwarded header: %v", err) // TODO change to slog on next branch
+			continue
+		}
+		if len(hosts) > 0 {
+			return hosts[0], true
+		}
 	}
-	return fwd["host"][0], true
+	return "", false
 }
 
 func StaticIssuer(issuer string) func(bool) (IssuerFromRequest, error) {


Test patch:
diff --git a/pkg/op/config_test.go b/pkg/op/config_test.go
index dcafc3a..d739348 100644
--- a/pkg/op/config_test.go
+++ b/pkg/op/config_test.go
@@ -1,6 +1,7 @@
 package op
 
 import (
+	"net/http"
 	"net/http/httptest"
 	"net/url"
 	"testing"
@@ -264,9 +265,10 @@ func TestIssuerFromHost(t *testing.T) {
 
 func TestIssuerFromForwardedOrHost(t *testing.T) {
 	type args struct {
-		path      string
-		target    string
-		forwarded []string
+		path   string
+		opts   []IssuerFromOption
+		target string
+		header map[string][]string
 	}
 	type res struct {
 		issuer string
@@ -279,9 +281,9 @@ func TestIssuerFromForwardedOrHost(t *testing.T) {
 		{
 			"header parse error",
 			args{
-				path:      "/custom/",
-				target:    "https://issuer.com",
-				forwarded: []string{"~~~"},
+				path:   "/custom/",
+				target: "https://issuer.com",
+				header: map[string][]string{"Forwarded": {"~~~~"}},
 			},
 			res{
 				issuer: "https://issuer.com/custom/",
@@ -303,9 +305,9 @@ func TestIssuerFromForwardedOrHost(t *testing.T) {
 			args{
 				path:   "/custom/",
 				target: "https://issuer.com",
-				forwarded: []string{
+				header: map[string][]string{"Forwarded": {
 					`by=identifier;for=identifier;proto=https`,
-				},
+				}},
 			},
 			res{
 				issuer: "https://issuer.com/custom/",
@@ -316,9 +318,9 @@ func TestIssuerFromForwardedOrHost(t *testing.T) {
 			args{
 				path:   "/custom/",
 				target: "https://issuer.com",
-				forwarded: []string{
+				header: map[string][]string{"Forwarded": {
 					`by=identifier;for=identifier;host=first.com;proto=https`,
-				},
+				}},
 			},
 			res{
 				issuer: "https://first.com/custom/",
@@ -329,9 +331,9 @@ func TestIssuerFromForwardedOrHost(t *testing.T) {
 			args{
 				path:   "/custom/",
 				target: "https://issuer.com",
-				forwarded: []string{
+				header: map[string][]string{"Forwarded": {
 					`by=identifier;for=identifier;host=first.com;proto=https,host=second.com`,
-				},
+				}},
 			},
 			res{
 				issuer: "https://first.com/custom/",
@@ -342,23 +344,45 @@ func TestIssuerFromForwardedOrHost(t *testing.T) {
 			args{
 				path:   "/custom/",
 				target: "https://issuer.com",
-				forwarded: []string{
+				header: map[string][]string{"Forwarded": {
 					`by=identifier;for=identifier;host=first.com;proto=https,host=second.com`,
 					`by=identifier;for=identifier;host=third.com;proto=https`,
-				},
+				}},
 			},
 			res{
 				issuer: "https://first.com/custom/",
 			},
 		},
+		{
+			"custom header first",
+			args{
+				path:   "/custom/",
+				target: "https://issuer.com",
+				header: map[string][]string{
+					"Forwarded": {
+						`by=identifier;for=identifier;host=first.com;proto=https,host=second.com`,
+						`by=identifier;for=identifier;host=third.com;proto=https`,
+					},
+					"X-Custom-Forwarded": {
+						`by=identifier;for=identifier;host=custom.com;proto=https,host=custom2.com`,
+					},
+				},
+				opts: []IssuerFromOption{
+					WithIssuerFromCustomHeaders("x-custom-forwarded"),
+				},
+			},
+			res{
+				issuer: "https://custom.com/custom/",
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			issuer, err := IssuerFromForwardedOrHost(tt.args.path)(false)
+			issuer, err := IssuerFromForwardedOrHost(tt.args.path, tt.args.opts...)(false)
 			require.NoError(t, err)
 			req := httptest.NewRequest("", tt.args.target, nil)
-			if tt.args.forwarded != nil {
-				req.Header["Forwarded"] = tt.args.forwarded
+			for k, v := range tt.args.header {
+				req.Header[http.CanonicalHeaderKey(k)] = v
 			}
 			assert.Equal(t, tt.res.issuer, issuer(req))
 		})