feat: add skew protection to Frameworks API

packages/build/package.json

@@ -115,7 +115,8 @@
     "typescript": "^5.0.0",
     "uuid": "^11.0.0",
     "yaml": "^2.8.0",
-    "yargs": "^17.6.0"
+    "yargs": "^17.6.0",
+    "zod": "^3.25.76"
   },
   "devDependencies": {
     "@netlify/nock-udp": "^5.0.1",

packages/build/src/plugins_core/edge_functions/index.ts

@@ -8,7 +8,7 @@ import { Metric } from '../../core/report_metrics.js'
 import { log, reduceLogLines } from '../../log/logger.js'
 import { logFunctionsToBundle } from '../../log/messages/core_steps.js'
 import {
-  FRAMEWORKS_API_EDGE_FUNCTIONS_ENDPOINT,
+  FRAMEWORKS_API_EDGE_FUNCTIONS_PATH,
   FRAMEWORKS_API_EDGE_FUNCTIONS_IMPORT_MAP,
 } from '../../utils/frameworks_api.js'
 
@@ -52,7 +52,7 @@ const coreStep = async function ({
   const internalSrcPath = resolve(buildDir, internalSrcDirectory)
   const distImportMapPath = join(dirname(internalSrcPath), IMPORT_MAP_FILENAME)
   const srcPath = srcDirectory ? resolve(buildDir, srcDirectory) : undefined
-  const frameworksAPISrcPath = resolve(buildDir, packagePath || '', FRAMEWORKS_API_EDGE_FUNCTIONS_ENDPOINT)
+  const frameworksAPISrcPath = resolve(buildDir, packagePath || '', FRAMEWORKS_API_EDGE_FUNCTIONS_PATH)
   const generatedFunctionPaths = [internalSrcPath]
 
   if (await pathExists(frameworksAPISrcPath)) {
@@ -62,7 +62,7 @@ const coreStep = async function ({
   const frameworkImportMap = resolve(
     buildDir,
     packagePath || '',
-    FRAMEWORKS_API_EDGE_FUNCTIONS_ENDPOINT,
+    FRAMEWORKS_API_EDGE_FUNCTIONS_PATH,
     FRAMEWORKS_API_EDGE_FUNCTIONS_IMPORT_MAP,
   )
 
@@ -170,7 +170,7 @@ const hasEdgeFunctionsDirectories = async function ({
     return true
   }
 
-  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_EDGE_FUNCTIONS_ENDPOINT)
+  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_EDGE_FUNCTIONS_PATH)
 
   return await pathExists(frameworkFunctionsSrc)
 }

packages/build/src/plugins_core/frameworks_api/index.ts

@@ -1,9 +1,14 @@
+import { promises as fs } from 'node:fs'
+import { dirname, resolve } from 'node:path'
+
 import { mergeConfigs } from '@netlify/config'
 
 import type { NetlifyConfig } from '../../index.js'
 import { getConfigMutations } from '../../plugins/child/diff.js'
+import { DEPLOY_CONFIG_DIST_PATH, FRAMEWORKS_API_SKEW_PROTECTION_PATH } from '../../utils/frameworks_api.js'
 import { CoreStep, CoreStepFunction } from '../types.js'
 
+import { loadSkewProtectionConfig } from './skew_protection.js'
 import { filterConfig, loadConfigFile } from './util.js'
 
 // The properties that can be set using this API. Each element represents a
@@ -26,6 +31,30 @@ const ALLOWED_PROPERTIES = [
 // a special notation where `redirects!` represents "forced redirects", etc.
 const OVERRIDE_PROPERTIES = new Set(['redirects!'])
 
+// Looks for a skew protection configuration file. If found, the file is loaded
+// and validated against the schema, throwing a build error if validation
+// fails. If valid, the contents are written to the edge redirects file.
+const handleSkewProtection = async (buildDir: string, packagePath?: string) => {
+  const inputPath = resolve(buildDir, packagePath ?? '', FRAMEWORKS_API_SKEW_PROTECTION_PATH)
+  const outputPath = resolve(buildDir, packagePath ?? '', DEPLOY_CONFIG_DIST_PATH)
+
+  const skewProtectionConfig = await loadSkewProtectionConfig(inputPath)
+  if (!skewProtectionConfig) {
+    return
+  }
+
+  const edgeRedirects = {
+    skew_protection: skewProtectionConfig,
+  }
+
+  try {
+    await fs.mkdir(dirname(outputPath), { recursive: true })
+    await fs.writeFile(outputPath, JSON.stringify(edgeRedirects))
+  } catch (error) {
+    throw new Error('Failed to process skew protection configuration', { cause: error })
+  }
+}
+
 const coreStep: CoreStepFunction = async function ({
   buildDir,
   netlifyConfig,
@@ -34,6 +63,7 @@ const coreStep: CoreStepFunction = async function ({
     // no-op
   },
 }) {
+  await handleSkewProtection(buildDir, packagePath)
   let config: Partial<NetlifyConfig> | undefined
 
   try {

packages/build/src/plugins_core/frameworks_api/skew_protection.ts

@@ -0,0 +1,54 @@
+import { promises as fs } from 'node:fs'
+
+import { z } from 'zod'
+
+const deployIDSourceTypeSchema = z.enum(['cookie', 'header', 'query'])
+
+const deployIDSourceSchema = z.object({
+  type: deployIDSourceTypeSchema,
+  name: z.string(),
+})
+
+const skewProtectionConfigSchema = z.object({
+  patterns: z.array(z.string()),
+  sources: z.array(deployIDSourceSchema),
+})
+
+export type SkewProtectionConfig = z.infer<typeof skewProtectionConfigSchema>
+export type DeployIDSource = z.infer<typeof deployIDSourceSchema>
+export type DeployIDSourceType = z.infer<typeof deployIDSourceTypeSchema>
+
+const validateSkewProtectionConfig = (input: unknown): SkewProtectionConfig => {
+  const { data, error, success } = skewProtectionConfigSchema.safeParse(input)
+
+  if (success) {
+    return data
+  }
+
+  throw new Error(`Invalid skew protection configuration:\n\n${formatSchemaError(error)}`)
+}
+
+export const loadSkewProtectionConfig = async (configPath: string) => {
+  let parsedData: unknown
+
+  try {
+    const data = await fs.readFile(configPath, 'utf8')
+
+    parsedData = JSON.parse(data)
+  } catch (error) {
+    // If the file doesn't exist, this is a non-error.
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+      return
+    }
+
+    throw new Error('Invalid skew protection configuration', { cause: error })
+  }
+
+  return validateSkewProtectionConfig(parsedData)
+}
+
+const formatSchemaError = (error: z.ZodError) => {
+  const lines = error.issues.map((issue) => `- ${issue.path.join('.')}: ${issue.message}`)
+
+  return lines.join('\n')
+}

packages/build/src/plugins_core/frameworks_api/util.ts

@@ -4,11 +4,11 @@ import { resolve } from 'path'
 import isPlainObject from 'is-plain-obj'
 
 import type { NetlifyConfig } from '../../index.js'
-import { FRAMEWORKS_API_CONFIG_ENDPOINT } from '../../utils/frameworks_api.js'
+import { FRAMEWORKS_API_CONFIG_PATH } from '../../utils/frameworks_api.js'
 import { SystemLogger } from '../types.js'
 
 export const loadConfigFile = async (buildDir: string, packagePath?: string) => {
-  const configPath = resolve(buildDir, packagePath ?? '', FRAMEWORKS_API_CONFIG_ENDPOINT)
+  const configPath = resolve(buildDir, packagePath ?? '', FRAMEWORKS_API_CONFIG_PATH)
 
   try {
     const data = await fs.readFile(configPath, 'utf8')

packages/build/src/plugins_core/functions/index.ts

@@ -7,7 +7,7 @@ import { addErrorInfo } from '../../error/info.js'
 import { log } from '../../log/logger.js'
 import { type GeneratedFunction, getGeneratedFunctions } from '../../steps/return_values.js'
 import { logBundleResults, logFunctionsNonExistingDir, logFunctionsToBundle } from '../../log/messages/core_steps.js'
-import { FRAMEWORKS_API_FUNCTIONS_ENDPOINT } from '../../utils/frameworks_api.js'
+import { FRAMEWORKS_API_FUNCTIONS_PATH } from '../../utils/frameworks_api.js'
 
 import { getZipError } from './error.js'
 import { getUserAndInternalFunctions, validateFunctionsSrc } from './utils.js'
@@ -147,7 +147,7 @@ const coreStep = async function ({
   const functionsDist = resolve(buildDir, relativeFunctionsDist)
   const internalFunctionsSrc = resolve(buildDir, relativeInternalFunctionsSrc)
   const internalFunctionsSrcExists = await pathExists(internalFunctionsSrc)
-  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_FUNCTIONS_ENDPOINT)
+  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_FUNCTIONS_PATH)
   const frameworkFunctionsSrcExists = await pathExists(frameworkFunctionsSrc)
   const functionsSrcExists = await validateFunctionsSrc({ functionsSrc, relativeFunctionsSrc })
   const [userFunctions = [], internalFunctions = [], frameworkFunctions = []] = await getUserAndInternalFunctions({
@@ -240,7 +240,7 @@ const hasFunctionsDirectories = async function ({
     return true
   }
 
-  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_FUNCTIONS_ENDPOINT)
+  const frameworkFunctionsSrc = resolve(buildDir, packagePath || '', FRAMEWORKS_API_FUNCTIONS_PATH)
 
   if (await pathExists(frameworkFunctionsSrc)) {
     return true

packages/build/src/plugins_core/pre_cleanup/index.ts

@@ -2,11 +2,11 @@ import { rm } from 'node:fs/promises'
 import { resolve } from 'node:path'
 
 import { getBlobsDirs } from '../../utils/blobs.js'
-import { FRAMEWORKS_API_ENDPOINT } from '../../utils/frameworks_api.js'
+import { FRAMEWORKS_API_PATH } from '../../utils/frameworks_api.js'
 import { CoreStep, CoreStepFunction } from '../types.js'
 
 const coreStep: CoreStepFunction = async ({ buildDir, packagePath }) => {
-  const dirs = [...getBlobsDirs(buildDir, packagePath), resolve(buildDir, packagePath || '', FRAMEWORKS_API_ENDPOINT)]
+  const dirs = [...getBlobsDirs(buildDir, packagePath), resolve(buildDir, packagePath || '', FRAMEWORKS_API_PATH)]
 
   try {
     await Promise.all(dirs.map((dir) => rm(dir, { recursive: true, force: true })))

packages/build/src/utils/blobs.ts

@@ -5,7 +5,7 @@ import { fdir } from 'fdir'
 
 import { DEFAULT_API_HOST } from '../core/normalize_flags.js'
 
-import { FRAMEWORKS_API_BLOBS_ENDPOINT } from './frameworks_api.js'
+import { FRAMEWORKS_API_BLOBS_PATH } from './frameworks_api.js'
 
 const LEGACY_BLOBS_PATH = '.netlify/blobs/deploy'
 const DEPLOY_CONFIG_BLOBS_PATH = '.netlify/deploy/v1/blobs/deploy'
@@ -60,7 +60,7 @@ export const getBlobsEnvironmentContext = ({
  */
 export const scanForBlobs = async function (buildDir: string, packagePath?: string) {
   // We start by looking for files using the Frameworks API.
-  const frameworkBlobsDir = path.resolve(buildDir, packagePath || '', FRAMEWORKS_API_BLOBS_ENDPOINT, 'deploy')
+  const frameworkBlobsDir = path.resolve(buildDir, packagePath || '', FRAMEWORKS_API_BLOBS_PATH, 'deploy')
   const frameworkBlobsDirScan = await new fdir().onlyCounts().crawl(frameworkBlobsDir).withPromise()
 
   if (frameworkBlobsDirScan.files > 0) {

packages/build/src/utils/frameworks_api.ts

@@ -2,12 +2,15 @@ import { basename, dirname, resolve, sep } from 'node:path'
 
 import { fdir } from 'fdir'
 
-export const FRAMEWORKS_API_ENDPOINT = '.netlify/v1'
-export const FRAMEWORKS_API_BLOBS_ENDPOINT = `${FRAMEWORKS_API_ENDPOINT}/blobs`
-export const FRAMEWORKS_API_CONFIG_ENDPOINT = `${FRAMEWORKS_API_ENDPOINT}/config.json`
-export const FRAMEWORKS_API_EDGE_FUNCTIONS_ENDPOINT = `${FRAMEWORKS_API_ENDPOINT}/edge-functions`
+export const FRAMEWORKS_API_PATH = '.netlify/v1'
+export const FRAMEWORKS_API_BLOBS_PATH = `${FRAMEWORKS_API_PATH}/blobs`
+export const FRAMEWORKS_API_CONFIG_PATH = `${FRAMEWORKS_API_PATH}/config.json`
+export const FRAMEWORKS_API_EDGE_FUNCTIONS_PATH = `${FRAMEWORKS_API_PATH}/edge-functions`
 export const FRAMEWORKS_API_EDGE_FUNCTIONS_IMPORT_MAP = 'import_map.json'
-export const FRAMEWORKS_API_FUNCTIONS_ENDPOINT = `${FRAMEWORKS_API_ENDPOINT}/functions`
+export const FRAMEWORKS_API_FUNCTIONS_PATH = `${FRAMEWORKS_API_PATH}/functions`
+export const FRAMEWORKS_API_SKEW_PROTECTION_PATH = `${FRAMEWORKS_API_PATH}/skew-protection.json`
+
+export const DEPLOY_CONFIG_DIST_PATH = '.netlify/deploy-config/deploy-config.json'
 
 type DirectoryTreeFiles = Map<string, string[]>
 

packages/build/tests/frameworks_api/fixtures/skew_protection_invalid/build.mjs

@@ -0,0 +1,8 @@
+import { mkdir, writeFile } from 'node:fs/promises'
+
+await mkdir('.netlify/v1', { recursive: true })
+
+await writeFile('.netlify/v1/skew-protection.json', JSON.stringify({
+  patterns: ["api"],
+  sources: [{ type: "invalid_type", name: "test" }]
+}))

packages/build/tests/frameworks_api/fixtures/skew_protection_invalid/netlify.toml

@@ -0,0 +1,2 @@
+[build]
+command = "node build.mjs"

packages/build/tests/frameworks_api/fixtures/skew_protection_malformed/build.mjs

@@ -0,0 +1,5 @@
+import { mkdir, writeFile } from 'node:fs/promises'
+
+await mkdir('.netlify/v1', { recursive: true })
+
+await writeFile('.netlify/v1/skew-protection.json', `{"patterns":`)

packages/build/tests/frameworks_api/fixtures/skew_protection_malformed/netlify.toml

@@ -0,0 +1,2 @@
+[build]
+command = "node build.mjs"

packages/build/tests/frameworks_api/fixtures/skew_protection_missing/build.mjs

@@ -0,0 +1 @@
+// No skew protection file created

packages/build/tests/frameworks_api/fixtures/skew_protection_missing/netlify.toml

@@ -0,0 +1,2 @@
+[build]
+command = "node build.mjs"

packages/build/tests/frameworks_api/fixtures/skew_protection_valid/build.mjs

@@ -0,0 +1,12 @@
+import { mkdir, writeFile } from 'node:fs/promises'
+
+await mkdir('.netlify/v1', { recursive: true })
+
+await writeFile('.netlify/v1/skew-protection.json', JSON.stringify({
+  patterns: ["/api/*", "/dashboard/*"],
+  sources: [
+    { type: "cookie", name: "nf_deploy_id" },
+    { type: "header", name: "x-nf-deploy-id" },
+    { type: "query", name: "deploy_id" }
+  ]
+}))

packages/build/tests/frameworks_api/fixtures/skew_protection_valid/netlify.toml

@@ -0,0 +1,2 @@
+[build]
+command = "node build.mjs"

packages/build/tests/frameworks_api/tests.js

@@ -151,3 +151,56 @@ test('Removes any leftover files from a previous build', async (t) => {
     remote_images: ['domain1.from-toml.netlify', 'domain2.from-toml.netlify'],
   })
 })
+
+test('Throws an error if the skew protection configuration file is invalid', async (t) => {
+  const { output, success } = await new Fixture('./fixtures/skew_protection_invalid').runWithBuildAndIntrospect()
+  t.false(success)
+  t.true(output.includes('Invalid skew protection configuration'))
+  t.true(
+    output.includes(
+      `sources.0.type: Invalid enum value. Expected 'cookie' | 'header' | 'query', received 'invalid_type'`,
+    ),
+  )
+})
+
+test('Throws an error if the skew protection configuration file is malformed', async (t) => {
+  const { output, success } = await new Fixture('./fixtures/skew_protection_malformed').runWithBuildAndIntrospect()
+  t.false(success)
+  t.true(output.includes('Invalid skew protection configuration'))
+})
+
+test('Does not create dist file when skew protection file is missing', async (t) => {
+  const fixture = new Fixture('./fixtures/skew_protection_missing')
+  const { success } = await fixture.runWithBuildAndIntrospect()
+  const distPath = resolve(fixture.repositoryRoot, '.netlify/deploy-config/deploy-config.json')
+  t.true(success)
+
+  try {
+    await fs.access(distPath)
+    t.fail('Dist file should not exist when skew protection file is missing')
+  } catch (error) {
+    t.is(error.code, 'ENOENT')
+  }
+})
+
+test('Creates dist file when valid skew protection configuration is provided', async (t) => {
+  const fixture = new Fixture('./fixtures/skew_protection_valid')
+  const { success } = await fixture.runWithBuildAndIntrospect()
+  const distPath = resolve(fixture.repositoryRoot, '.netlify/deploy-config/deploy-config.json')
+
+  t.true(success)
+
+  const distContent = await fs.readFile(distPath, 'utf8')
+  const config = JSON.parse(distContent)
+
+  t.deepEqual(config, {
+    skew_protection: {
+      patterns: ['/api/*', '/dashboard/*'],
+      sources: [
+        { type: 'cookie', name: 'nf_deploy_id' },
+        { type: 'header', name: 'x-nf-deploy-id' },
+        { type: 'query', name: 'deploy_id' },
+      ],
+    },
+  })
+})