fix: enforce MCP OAuth callback state before errors (#775)
This commit is contained in:
Kevin Codex
GitHub
61
src/services/mcp/auth.test.ts
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61
src/services/mcp/auth.test.ts
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@@ -0,0 +1,61 @@
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import assert from 'node:assert/strict'
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import test from 'node:test'
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import { validateOAuthCallbackParams } from './auth.js'
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test('OAuth callback rejects error parameters before state validation can be bypassed', () => {
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const result = validateOAuthCallbackParams(
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{
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error: 'access_denied',
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error_description: 'denied by provider',
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},
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'expected-state',
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)
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assert.deepEqual(result, { type: 'state_mismatch' })
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})
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test('OAuth callback accepts provider errors only when state matches', () => {
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const result = validateOAuthCallbackParams(
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{
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state: 'expected-state',
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error: 'access_denied',
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error_description: 'denied by provider',
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error_uri: 'https://example.test/error',
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},
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'expected-state',
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)
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assert.deepEqual(result, {
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type: 'error',
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error: 'access_denied',
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errorDescription: 'denied by provider',
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errorUri: 'https://example.test/error',
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message:
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'OAuth error: access_denied - denied by provider (See: https://example.test/error)',
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})
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})
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test('OAuth callback accepts authorization codes only when state matches', () => {
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assert.deepEqual(
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validateOAuthCallbackParams(
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{
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state: 'expected-state',
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code: 'auth-code',
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},
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'expected-state',
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),
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{ type: 'code', code: 'auth-code' },
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)
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assert.deepEqual(
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validateOAuthCallbackParams(
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{
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state: 'wrong-state',
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code: 'auth-code',
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},
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'expected-state',
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),
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{ type: 'state_mismatch' },
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)
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})
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@@ -124,6 +124,74 @@ function redactSensitiveUrlParams(url: string): string {
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}
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}
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type OAuthCallbackParamValue = string | string[] | null | undefined
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type OAuthCallbackValidationResult =
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| { type: 'code'; code: string }
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| {
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type: 'error'
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error: string
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errorDescription: string
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errorUri: string
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message: string
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}
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| { type: 'missing_result' }
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| { type: 'state_mismatch' }
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function getFirstOAuthCallbackParam(
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value: OAuthCallbackParamValue,
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): string | undefined {
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if (Array.isArray(value)) {
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return value.find(item => item.length > 0)
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}
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return value && value.length > 0 ? value : undefined
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}
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export function validateOAuthCallbackParams(
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params: {
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code?: OAuthCallbackParamValue
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state?: OAuthCallbackParamValue
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error?: OAuthCallbackParamValue
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error_description?: OAuthCallbackParamValue
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error_uri?: OAuthCallbackParamValue
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},
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oauthState: string,
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): OAuthCallbackValidationResult {
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const code = getFirstOAuthCallbackParam(params.code)
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const state = getFirstOAuthCallbackParam(params.state)
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const error = getFirstOAuthCallbackParam(params.error)
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const errorDescription =
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getFirstOAuthCallbackParam(params.error_description) ?? ''
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const errorUri = getFirstOAuthCallbackParam(params.error_uri) ?? ''
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if (state !== oauthState) {
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return { type: 'state_mismatch' }
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}
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if (error) {
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let message = `OAuth error: ${error}`
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if (errorDescription) {
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message += ` - ${errorDescription}`
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}
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if (errorUri) {
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message += ` (See: ${errorUri})`
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}
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return {
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type: 'error',
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error,
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errorDescription,
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errorUri,
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message,
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}
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}
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if (code) {
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return { type: 'code', code }
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}
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return { type: 'missing_result' }
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}
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/**
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* Some OAuth servers (notably Slack) return HTTP 200 for all responses,
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* signaling errors via the JSON body instead. The SDK's executeTokenRequest
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@@ -1058,30 +1126,31 @@ export async function performMCPOAuthFlow(
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options.onWaitingForCallback((callbackUrl: string) => {
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try {
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const parsed = new URL(callbackUrl)
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const code = parsed.searchParams.get('code')
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const state = parsed.searchParams.get('state')
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const error = parsed.searchParams.get('error')
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if (error) {
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const errorDescription =
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parsed.searchParams.get('error_description') || ''
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cleanup()
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rejectOnce(
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new Error(`OAuth error: ${error} - ${errorDescription}`),
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const result = validateOAuthCallbackParams(
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{
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code: parsed.searchParams.get('code'),
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state: parsed.searchParams.get('state'),
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error: parsed.searchParams.get('error'),
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error_description:
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parsed.searchParams.get('error_description'),
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error_uri: parsed.searchParams.get('error_uri'),
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},
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oauthState,
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)
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if (result.type === 'state_mismatch') {
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// Ignore so a stray or malicious URL cannot cancel an active flow.
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return
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}
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if (!code) {
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// Not a valid callback URL, ignore so the user can try again
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if (result.type === 'missing_result') {
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// Not a valid callback URL, ignore so the user can try again.
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return
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}
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if (state !== oauthState) {
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if (result.type === 'error') {
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cleanup()
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rejectOnce(
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new Error('OAuth state mismatch - possible CSRF attack'),
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)
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rejectOnce(new Error(result.message))
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return
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}
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@@ -1090,7 +1159,7 @@ export async function performMCPOAuthFlow(
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`Received auth code via manual callback URL`,
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)
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cleanup()
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resolveOnce(code)
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resolveOnce(result.code)
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} catch {
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// Invalid URL, ignore so the user can try again
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}
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@@ -1101,53 +1170,49 @@ export async function performMCPOAuthFlow(
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const parsedUrl = parse(req.url || '', true)
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if (parsedUrl.pathname === '/callback') {
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const code = parsedUrl.query.code as string
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const state = parsedUrl.query.state as string
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const error = parsedUrl.query.error
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const errorDescription = parsedUrl.query.error_description as string
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const errorUri = parsedUrl.query.error_uri as string
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const result = validateOAuthCallbackParams(
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parsedUrl.query,
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oauthState,
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)
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// Validate OAuth state to prevent CSRF attacks
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if (!error && state !== oauthState) {
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if (result.type === 'state_mismatch') {
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res.writeHead(400, { 'Content-Type': 'text/html' })
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res.end(
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`<h1>Authentication Error</h1><p>Invalid state parameter. Please try again.</p><p>You can close this window.</p>`,
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)
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cleanup()
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rejectOnce(new Error('OAuth state mismatch - possible CSRF attack'))
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return
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}
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if (error) {
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if (result.type === 'missing_result') {
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res.writeHead(400, { 'Content-Type': 'text/html' })
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res.end(
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`<h1>Authentication Error</h1><p>Missing OAuth result. Please try again.</p><p>You can close this window.</p>`,
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)
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return
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}
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if (result.type === 'error') {
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res.writeHead(200, { 'Content-Type': 'text/html' })
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// Sanitize error messages to prevent XSS
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const sanitizedError = xss(String(error))
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const sanitizedErrorDescription = errorDescription
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? xss(String(errorDescription))
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const sanitizedError = xss(result.error)
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const sanitizedErrorDescription = result.errorDescription
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? xss(result.errorDescription)
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: ''
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res.end(
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`<h1>Authentication Error</h1><p>${sanitizedError}: ${sanitizedErrorDescription}</p><p>You can close this window.</p>`,
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)
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cleanup()
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let errorMessage = `OAuth error: ${error}`
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if (errorDescription) {
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errorMessage += ` - ${errorDescription}`
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}
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if (errorUri) {
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errorMessage += ` (See: ${errorUri})`
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}
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rejectOnce(new Error(errorMessage))
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rejectOnce(new Error(result.message))
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return
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}
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if (code) {
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res.writeHead(200, { 'Content-Type': 'text/html' })
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res.end(
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`<h1>Authentication Successful</h1><p>You can close this window. Return to Claude Code.</p>`,
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)
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cleanup()
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resolveOnce(code)
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}
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resolveOnce(result.code)
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}
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})
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