feat: auto-detect realm from request Host header

.changeset/realm-auto-detection.md

@@ -0,0 +1,5 @@
+---
+'mppx': patch
+---
+
+Added `realm` auto-detection from the request `Host` header when not explicitly configured. Resolution order: explicit value → env vars (`MPP_REALM`, `FLY_APP_NAME`, `VERCEL_URL`, etc.) → request URL hostname → `"MPP Payment"` fallback with a one-time warning. Removed the hard-coded `"MPP Payment"` default and deprioritized `HOST`/`HOSTNAME` env vars in favor of platform-specific alternatives.

.github/workflows/verify.yml

@@ -47,6 +47,9 @@ jobs:
       matrix:
         shard: [1/3, 2/3, 3/3]
     env:
+      # GitHub-hosted runners are ephemeral, so we can skip the Ryuk sidecar
+      # and avoid Docker Hub rate limits on testcontainers/ryuk pulls.
+      TESTCONTAINERS_RYUK_DISABLED: true
       VITE_TEMPO_TAG: sha-20aecec
     steps:
       - name: Clone repository

src/internal/env.test.ts

@@ -5,8 +5,8 @@ afterEach(() => {
 })
 
 describe('Env.get', () => {
-  test('returns default realm when no env vars are set', () => {
-    expect(Env.get('realm')).toBe('MPP Payment')
+  test('returns undefined when no env vars are set', () => {
+    expect(Env.get('realm')).toBeUndefined()
   })
 
   test('returns undefined when MPP_SECRET_KEY is not set', () => {
@@ -18,25 +18,25 @@ describe('Env.get', () => {
     expect(Env.get('secretKey')).toBe('sk_live_abc123')
   })
 
+  test('MPP_REALM takes precedence over platform vars', () => {
+    vi.stubEnv('MPP_REALM', 'custom-realm')
+    vi.stubEnv('FLY_APP_NAME', 'fly-app')
+    expect(Env.get('realm')).toBe('custom-realm')
+  })
+
   test('returns FLY_APP_NAME when set', () => {
     vi.stubEnv('FLY_APP_NAME', 'my-fly-app')
     expect(Env.get('realm')).toBe('my-fly-app')
   })
 
-  test('FLY_APP_NAME takes precedence over HOST', () => {
+  test('FLY_APP_NAME takes precedence over VERCEL_URL', () => {
     vi.stubEnv('FLY_APP_NAME', 'fly-app')
-    vi.stubEnv('HOST', 'my-host')
+    vi.stubEnv('VERCEL_URL', 'my-app.vercel.app')
     expect(Env.get('realm')).toBe('fly-app')
   })
 
-  test('HOST takes precedence over MPP_REALM', () => {
-    vi.stubEnv('HOST', 'my-host')
-    vi.stubEnv('MPP_REALM', 'custom-realm')
-    expect(Env.get('realm')).toBe('my-host')
-  })
-
   test('falls through to later vars when earlier ones are unset', () => {
-    vi.stubEnv('MPP_REALM', 'fallback-realm')
-    expect(Env.get('realm')).toBe('fallback-realm')
+    vi.stubEnv('VERCEL_URL', 'my-app.vercel.app')
+    expect(Env.get('realm')).toBe('my-app.vercel.app')
   })
 })

src/internal/env.ts

@@ -1,11 +1,9 @@
 /** Map of configuration keys to environment variable names, checked in order. */
 const variables = {
   realm: [
+    'MPP_REALM',
     'FLY_APP_NAME',
     'HEROKU_APP_NAME',
-    'HOST',
-    'HOSTNAME',
-    'MPP_REALM',
     'RAILWAY_PUBLIC_DOMAIN',
     'RENDER_EXTERNAL_HOSTNAME',
     'VERCEL_URL',
@@ -15,9 +13,7 @@ const variables = {
 } as const satisfies Record<string, readonly string[]>
 
 /** Fallback values when no environment variable is set. */
-const defaults = {
-  realm: 'MPP Payment',
-} as const satisfies Partial<Record<keyof typeof variables, string>>
+const defaults = {} as const satisfies Partial<Record<keyof typeof variables, string>>
 
 /**
  * Resolves a configuration value from environment variables.

src/server/Mppx.test.ts

@@ -1741,3 +1741,219 @@ describe('withReceipt', () => {
     server.close()
   })
 })
+
+describe('realm auto-detection', () => {
+  beforeEach(() => {
+    // Clear all env vars that Env.get('realm') probes so realm falls through to request detection
+    for (const name of [
+      'MPP_REALM',
+      'FLY_APP_NAME',
+      'HEROKU_APP_NAME',
+      'RAILWAY_PUBLIC_DOMAIN',
+      'RENDER_EXTERNAL_HOSTNAME',
+      'VERCEL_URL',
+      'WEBSITE_HOSTNAME',
+    ])
+      vi.stubEnv(name, '')
+  })
+
+  afterEach(() => {
+    vi.unstubAllEnvs()
+  })
+
+  const mockMethod = Method.toServer(
+    Method.from({
+      name: 'mock',
+      intent: 'charge',
+      schema: {
+        credential: { payload: z.object({ token: z.string() }) },
+        request: z.object({ amount: z.string(), currency: z.string(), recipient: z.string() }),
+      },
+    }),
+    {
+      async verify() {
+        return {
+          method: 'mock',
+          reference: 'ref',
+          status: 'success' as const,
+          timestamp: new Date().toISOString(),
+        }
+      },
+    },
+  )
+
+  test.each([
+    { url: 'https://mpp.dev/resource', expected: 'mpp.dev' },
+    { url: 'https://api.example.com/v1/resource', expected: 'api.example.com' },
+    { url: 'https://localhost:8787/resource', expected: 'localhost' },
+    { url: 'https://MPP.DEV/resource', expected: 'mpp.dev' },
+    { url: 'http://staging.mpp.dev:3000/api', expected: 'staging.mpp.dev' },
+  ])('derives realm "$expected" from $url', async ({ url, expected }) => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+
+    const result = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(new Request(url))
+
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    expect(challenge.realm).toBe(expected)
+  })
+
+  test('credential verifies across different casing of same host', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+
+    const chargeOpts = {
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    }
+
+    // Get challenge with uppercase host
+    const result = await handler.charge(chargeOpts)(new Request('https://MPP.DEV/resource'))
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    const credential = Credential.from({ challenge, payload: { token: 'valid' } })
+
+    // Verify with lowercase host — should match since both normalize
+    const verifyResult = await handler.charge(chargeOpts)(
+      new Request('https://mpp.dev/resource', {
+        headers: { Authorization: Credential.serialize(credential) },
+      }),
+    )
+    expect(verifyResult.status).toBe(200)
+  })
+
+  test('explicit realm takes precedence over request url', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], realm: 'explicit.example.com', secretKey })
+
+    const request = new Request('https://other.example.com/resource')
+    const result = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(request)
+
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    expect(challenge.realm).toBe('explicit.example.com')
+  })
+
+  test('challenge and verification use same auto-detected realm', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+
+    const url = 'https://mpp.dev/resource'
+
+    // Get challenge
+    const result = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(new Request(url))
+
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    const credential = Credential.from({ challenge, payload: { token: 'valid' } })
+
+    // Replay with credential from same host — should verify
+    const verifyResult = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(new Request(url, { headers: { Authorization: Credential.serialize(credential) } }))
+
+    expect(verifyResult.status).toBe(200)
+  })
+
+  test('credential from one host rejected at different host', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+
+    // Get challenge from host A
+    const result = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(new Request('https://host-a.example.com/resource'))
+
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    const credential = Credential.from({ challenge, payload: { token: 'valid' } })
+
+    // Present at host B — realm mismatch should reject
+    const verifyResult = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(
+      new Request('https://host-b.example.com/resource', {
+        headers: { Authorization: Credential.serialize(credential) },
+      }),
+    )
+
+    expect(verifyResult.status).toBe(402)
+  })
+
+  test('realm undefined on handler when not explicitly set', () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+    expect(handler.realm).toBeUndefined()
+  })
+
+  test('falls back to default realm when input has no url', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+    const handle = handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })
+
+    // Simulate a non-HTTP input with no .url — should warn and use fallback
+    const result = await handle({} as any)
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+    const challenge = Challenge.fromResponse(result.challenge)
+    expect(challenge.realm).toBe('MPP Payment')
+  })
+
+  test('cross-host rejection reports realm mismatch', async () => {
+    const handler = Mppx.create({ methods: [mockMethod], secretKey })
+
+    const result = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(new Request('https://host-a.example.com/resource'))
+
+    expect(result.status).toBe(402)
+    if (result.status !== 402) throw new Error()
+
+    const challenge = Challenge.fromResponse(result.challenge)
+    const credential = Credential.from({ challenge, payload: { token: 'valid' } })
+
+    const verifyResult = await handler.charge({
+      amount: '100',
+      currency: '0x0000000000000000000000000000000000000001',
+      recipient: '0x0000000000000000000000000000000000000002',
+    })(
+      new Request('https://host-b.example.com/resource', {
+        headers: { Authorization: Credential.serialize(credential) },
+      }),
+    )
+
+    expect(verifyResult.status).toBe(402)
+    if (verifyResult.status !== 402) throw new Error()
+    const body = (await verifyResult.challenge.json()) as { detail: string }
+    expect(body.detail).toContain('realm')
+  })
+})

src/server/Mppx.ts

@@ -153,7 +153,7 @@ export function create<
   const transport extends Transport.AnyTransport = Transport.Http,
 >(config: create.Config<methods, transport>): Mppx<methods, transport> {
   const {
-    realm = Env.get('realm') ?? 'MPP Payment',
+    realm = Env.get('realm'),
     secretKey = Env.get('secretKey'),
     transport = Transport.http() as transport,
   } = config
@@ -222,7 +222,7 @@ export function create<
   return {
     methods,
     compose: composeFn,
-    realm: realm as string,
+    realm: realm as string | undefined,
     transport,
     ...handlers,
   } as never
@@ -235,7 +235,7 @@ export declare namespace create {
   > = {
     /** Array of configured methods. @example [tempo()] */
     methods: methods
-    /** Server realm (e.g., hostname). Auto-detected from environment variables (`MPP_REALM`, `VERCEL_URL`, `RAILWAY_PUBLIC_DOMAIN`, `RENDER_EXTERNAL_HOSTNAME`, `HOST`, `HOSTNAME`), falling back to `"localhost"`. */
+    /** Server realm (e.g., hostname). Resolution order: explicit value > env vars (`MPP_REALM`, `FLY_APP_NAME`, `VERCEL_URL`, etc.) > request URL hostname > `"MPP Payment"`. */
     realm?: string | undefined
     /** Secret key for HMAC-bound challenge IDs for stateless verification. Auto-detected from `MPP_SECRET_KEY` environment variable. Throws if neither provided nor set. */
     secretKey?: string | undefined
@@ -283,14 +283,17 @@ function createMethodFn(parameters: createMethodFn.Parameters): createMethodFn.R
             : merged
         ) as never
 
+        // Resolve realm: explicit > env var > request Host header.
+        const effectiveRealm = realm ?? resolveRealmFromRequest(input)
+
         // Recompute challenge from options. The HMAC-bound ID means we don't need to
         // store challenges server-side—if the client echoes back a credential with
         // a matching ID, we know it was issued by us with these exact parameters.
         const challenge = Challenge.fromMethod(method, {
           description,
           expires,
           meta,
-          realm,
+          realm: effectiveRealm,
           request,
           secretKey,
         })
@@ -483,7 +486,7 @@ declare namespace createMethodFn {
   > = {
     defaults?: defaults
     method: method
-    realm: string
+    realm: string | undefined
     request?: Method.RequestFn<method>
     respond?: Method.RespondFn<method>
     secretKey: string
@@ -498,6 +501,34 @@ declare namespace createMethodFn {
   > = MethodFn<method, transport, defaults>
 }
 
+const defaultRealm = 'MPP Payment'
+const Warnings = {
+  realmFallback: 'realm-fallback',
+} as const
+
+const _warned = new Set<string>()
+function warnOnce(key: string, message: string) {
+  if (_warned.has(key)) return
+  _warned.add(key)
+  console.warn(`[mppx] ${message}`)
+}
+
+/** Extracts hostname from the request URL, falling back to a default. */
+function resolveRealmFromRequest(input: unknown): string {
+  try {
+    const url = typeof (input as any)?.url === 'string' ? (input as any).url : undefined
+    if (url) {
+      const { protocol, hostname } = new URL(url)
+      if (/^https?:$/.test(protocol) && hostname) return hostname
+    }
+  } catch {}
+  warnOnce(
+    Warnings.realmFallback,
+    `Could not auto-detect realm from request. Falling back to "${defaultRealm}". Set \`realm\` in Mppx.create() or the MPP_REALM env var.`,
+  )
+  return defaultRealm
+}
+
 export type MethodFn<
   method extends Method.Method,
   transport extends Transport.AnyTransport,