Discriminated types from zod schemas are not inferred properly in custom plugins #4513
Closed as not planned
Description
Is this suited for github?
- Yes, this is suited for github
To Reproduce
- Create a custom better-auth plugin with an endpoint that has zod schema that uses discriminated unions.
- Create the client plugin by inferring the server plugin.
- Now create a auth client using this client plugin.
- Call the endpoint and try to pass params based on the discriminated schema.
- Only common properties can be type safely passed here.
Current vs. Expected behavior
I expected the discriminated types to work but only the common properties in the union were available when using the auth client.
For eg:
sendVerificationOTP: createAuthEndpoint(
'/my-plugin-auth/send-verification-otp',
{
method: 'POST',
body: z.union([
z.object({
purpose: z.literal('login'),
mobileNumber: mobileNumberZod,
password: z.string().trim(),
}),
z.object({
purpose: z.literal('register'),
mobileNumber: mobileNumberZod,
email: emailZod,
}),
z.object({
purpose: z.literal('phone-verification'),
mobileNumber: mobileNumberZod,
}),
z.object({
purpose: z.literal('email-verification'),
email: emailZod,
}),
z.object({
purpose: z.literal('password-reset'),
mobileNumber: mobileNumberZod,
})
]),
....
}Now if we infer the types and create a client plugin and auth client
const myPluginAuth = () => {
return {
id: 'my-plugin',
$InferServerPlugin: {} as ReturnType<typeof myAuthPlugin>
} satisfies BetterAuthClientPlugin
}const authClient = createAuthClient({
baseURL: 'http://localhost:port', // The base URL of your auth server,
plugins: [myAuthClient()]
})
authClient.myPluginAuth.sendVerificationOtp({
purpose: 'email-verification', // Only this field is inferred since it is common
email: 'test@example.com' // This field is not inferred
})What version of Better Auth are you using?
1.3.8
System info
{
"system": {
"platform": "darwin",
"arch": "arm64",
"version": "Darwin Kernel Version 24.5.0: Tue Apr 22 19:53:27 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6041",
"release": "24.5.0",
"cpuCount": 16,
"cpuModel": "Apple M4 Max",
"totalMemory": "48.00 GB",
"freeMemory": "1.81 GB"
},
"node": {
"version": "v22.14.0",
"env": "development"
},
"packageManager": {
"name": "pnpm",
"version": "9.7.1"
},
"frameworks": null,
"databases": null,
"betterAuth": {
"version": "0.1.0",
"config": null
}
}Which area(s) are affected? (Select all that apply)
Client
Auth config (if applicable)
Additional context
No response