feat(server): csp template (#2856)

Implements the ability for advanced users to override the CSP and easily include the required nonce.

config.template.yml

@@ -71,6 +71,12 @@ server:
     ## The path to the DER base64/PEM format public certificate.
     certificate: ""
 
+  ## Server headers configuration/customization.
+  headers:
+
+    ## The CSP Template. Read the docs.
+    csp_template: ""
+
 ##
 ## Log Configuration
 ##

docs/configuration/server.md

@@ -24,6 +24,8 @@ server:
   tls:
     key: ""
     certificate: ""
+  headers:
+    csp_template: ""
 ```
 
 ## Options
@@ -209,6 +211,25 @@ required: situational
 
 The path to the public certificate for TLS connections. Must be in DER base64/PEM format.
 
+
+### headers
+
+#### csp_template
+<div markdown="1">
+type: string
+{: .label .label-config .label-purple } 
+default: ""
+{: .label .label-config .label-blue }
+required: no
+{: .label .label-config .label-green }
+</div>
+
+This customizes the value of the Content-Security-Policy header. It will replace all instances of `${NONCE}` with the 
+nonce value of the Authelia react bundle. This is an advanced option to customize and you should do sufficient research 
+about how browsers utilize and understand this header before attempting to customize it.
+
+For example, the default CSP template is `default-src 'self'; object-src 'none'; style-src 'self' 'nonce-${NONCE}'`.
+
 ## Additional Notes
 
 ### Buffer Sizes

internal/configuration/config.template.yml

@@ -71,6 +71,12 @@ server:
     ## The path to the DER base64/PEM format public certificate.
     certificate: ""
 
+  ## Server headers configuration/customization.
+  headers:
+
+    ## The CSP Template. Read the docs.
+    csp_template: ""
+
 ##
 ## Log Configuration
 ##

internal/configuration/schema/server.go

@@ -13,6 +13,7 @@ type ServerConfiguration struct {
 	DisableHealthcheck bool   `koanf:"disable_healthcheck"`
 
 	TLS     ServerTLSConfiguration     `koanf:"tls"`
+	Headers ServerHeadersConfiguration `koanf:"headers"`
 }
 
 // ServerTLSConfiguration represents the configuration of the http servers TLS options.
@@ -21,6 +22,11 @@ type ServerTLSConfiguration struct {
 	Key         string `koanf:"key"`
 }
 
+// ServerHeadersConfiguration represents the customization of the http server headers.
+type ServerHeadersConfiguration struct {
+	CSPTemplate string `koanf:"csp_template"`
+}
+
 // DefaultServerConfiguration represents the default values of the ServerConfiguration.
 var DefaultServerConfiguration = ServerConfiguration{
 	Host:            "0.0.0.0",

internal/configuration/validator/const.go

@@ -171,6 +171,7 @@ var ValidKeys = []string{
 	"server.disable_healthcheck",
 	"server.tls.key",
 	"server.tls.certificate",
+	"server.headers.csp_template",
 
 	// TOTP Keys.
 	"totp.issuer",

internal/server/const.go

@@ -23,3 +23,9 @@ X_AUTHELIA_HEALTHCHECK_HOST=%s
 X_AUTHELIA_HEALTHCHECK_PORT=%d
 X_AUTHELIA_HEALTHCHECK_PATH=%s
 `
+
+const (
+	cspDefaultTemplate    = "default-src 'self'; object-src 'none'; style-src 'self' 'nonce-%s'"
+	cspDefaultDevTemplate = "default-src 'self' 'unsafe-eval'; object-src 'none'; style-src 'self' 'nonce-%s'"
+	cspNoncePlaceholder   = "${NONCE}"
+)

internal/server/template.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 	"text/template"
 
 	"github.com/authelia/authelia/v4/internal/logging"
@@ -71,11 +72,13 @@ func ServeTemplatedFile(publicDir, file, assetPath, duoSelfEnrollment, rememberM
 
 		switch {
 		case publicDir == swaggerAssets:
-			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf("base-uri 'self' ; default-src 'self' ; img-src 'self' https://validator.swagger.io data: ; object-src 'none' ; script-src 'self' 'unsafe-inline' 'nonce-%s' ; style-src 'self' 'nonce-%s'", nonce, nonce))
+			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf("base-uri 'self'; default-src 'self'; img-src 'self' https://validator.swagger.io data:; object-src 'none'; script-src 'self' 'unsafe-inline' 'nonce-%s'; style-src 'self' 'nonce-%s'", nonce, nonce))
+		case ctx.Configuration.Server.Headers.CSPTemplate != "":
+			ctx.Response.Header.Add("Content-Security-Policy", strings.ReplaceAll(ctx.Configuration.Server.Headers.CSPTemplate, cspNoncePlaceholder, nonce))
 		case os.Getenv("ENVIRONMENT") == dev:
-			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf("default-src 'self' 'unsafe-eval'; object-src 'none'; style-src 'self' 'nonce-%s'", nonce))
+			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf(cspDefaultDevTemplate, nonce))
 		default:
-			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf("default-src 'self' ; object-src 'none'; style-src 'self' 'nonce-%s'", nonce))
+			ctx.Response.Header.Add("Content-Security-Policy", fmt.Sprintf(cspDefaultTemplate, nonce))
 		}
 
 		err := tmpl.Execute(ctx.Response.BodyWriter(), struct{ Base, BaseURL, CSPNonce, DuoSelfEnrollment, LogoOverride, RememberMe, ResetPassword, Session, Theme string }{Base: base, BaseURL: baseURL, CSPNonce: nonce, DuoSelfEnrollment: duoSelfEnrollment, LogoOverride: logoOverride, RememberMe: rememberMe, ResetPassword: resetPassword, Session: session, Theme: theme})