identity/oidc: loopback redirect dynamic port (#13871)

* Add check for OIDC provider to permit a non-exact redirect URI from OIDC client if it is the IPv4 or IPv6 loopback address.

* Update changelog/13871.txt

Co-authored-by: Austin Gebauer <34121980+austingebauer@users.noreply.github.com>

* Update redirectURI check to match that for the OIDC auth method.

Co-authored-by: Austin Gebauer <34121980+austingebauer@users.noreply.github.com>

changelog/13871.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+identity/oidc: Adds support for port-agnostic validation of loopback IP redirect URIs.
+```

vault/identity_store_oidc_provider.go

@@ -1513,7 +1513,8 @@ func (i *IdentityStore) pathOIDCAuthorize(ctx context.Context, req *logical.Requ
 	if redirectURI == "" {
 		return authResponse("", state, ErrAuthInvalidRequest, "redirect_uri parameter is required")
 	}
-	if !strutil.StrListContains(client.RedirectURIs, redirectURI) {
+
+	if !validRedirect(redirectURI, client.RedirectURIs) {
 		return authResponse("", state, ErrAuthInvalidRedirectURI, "redirect_uri is not allowed for the client")
 	}
 

vault/identity_store_oidc_provider_util.go

@@ -0,0 +1,38 @@
+package vault
+
+import (
+	"net/url"
+
+	"github.com/hashicorp/go-secure-stdlib/strutil"
+)
+
+// validRedirect checks whether uri is in allowed using special handling for loopback uris.
+// Ref: https://tools.ietf.org/html/rfc8252#section-7.3
+func validRedirect(uri string, allowed []string) bool {
+	inputURI, err := url.Parse(uri)
+	if err != nil {
+		return false
+	}
+
+	// if uri isn't a loopback, just string search the allowed list
+	if !strutil.StrListContains([]string{"localhost", "127.0.0.1", "::1"}, inputURI.Hostname()) {
+		return strutil.StrListContains(allowed, uri)
+	}
+
+	// otherwise, search for a match in a port-agnostic manner, per the OAuth RFC.
+	inputURI.Host = inputURI.Hostname()
+
+	for _, a := range allowed {
+		allowedURI, err := url.Parse(a)
+		if err != nil {
+			return false
+		}
+		allowedURI.Host = allowedURI.Hostname()
+
+		if inputURI.String() == allowedURI.String() {
+			return true
+		}
+	}
+
+	return false
+}