Cannot pass custom fields defined in additionalFields to auth.api.signUpEmail() body due to incorrect TypeScript inference #2466

New Issue

GiteaMirror · 2026-03-13T09:56:32-05:00

GiteaMirror commented

2026-03-13 09:56:32 -05:00

Originally created by @GreedyPirate on GitHub (Dec 5, 2025).

Is this suited for github?

Yes, this is suited for github

To Reproduce

I'm using Better Auth with custom user fields configured via additionalFields:

user: {
  additionalFields: {
    country: { type: "string", required: true },
    // ... other fields
  }
}

According to the documentation, I should be able to pass these fields directly in the signup server side call like this:

await auth.api.signUpEmail({
  body: {
    email: "...",
    password: "...",
    name: "...",
    country: "US",        // ← custom field
  }
});

Current vs. Expected behavior

TS2769: No overload matches this call. The last overload gave the following error. Object literal may only specify known properties, and country does not exist in type

What version of Better Auth are you using?

1.4.5

System info

{
  "system": {
    "platform": "win32",
    "arch": "x64",
    "version": "Windows 10 Pro",
    "release": "10.0.19045",
    "cpuCount": 20,
    "cpuModel": "12th Gen Intel(R) Core(TM) i7-12700",
    "totalMemory": "47.75 GB",
    "freeMemory": "24.39 GB"
  },
  "node": {
    "version": "v22.13.1",
    "env": "development"
  },
  "packageManager": {
    "name": "npm",
  },
  "frameworks": [
    {
      "name": "next",
      "version": "16.0.6"
    },
    {
      "name": "react",
      "version": "19.2.0"
    }
  ],
  "databases": null,
  "betterAuth": {
    "version": "^1.4.5",
    "config": null
  }
}

Which area(s) are affected? (Select all that apply)

Backend

Auth config (if applicable)

import {betterAuth} from "better-auth"

export const auth = betterAuth({
    emailAndPassword: {
        enabled: true
    },
    user: {
        deleteUser: {
            enabled: true
        },
        additionalFields: {
            country: {
                type: "string",
                required: true
            }
        },
    }
});

Additional context

No response

Originally created by @GreedyPirate on GitHub (Dec 5, 2025). ### Is this suited for github? - [x] Yes, this is suited for github ### To Reproduce I'm using Better Auth with custom user fields configured via additionalFields: ```ts user: { additionalFields: { country: { type: "string", required: true }, // ... other fields } } ``` According to the documentation, I should be able to pass these fields directly in the signup **server side** call like this: ``` await auth.api.signUpEmail({ body: { email: "...", password: "...", name: "...", country: "US", // ← custom field } }); ``` ### Current vs. Expected behavior `TS2769: No overload matches this call. The last overload gave the following error. Object literal may only specify known properties, and country does not exist in type` ### What version of Better Auth are you using? 1.4.5 ### System info ```bash { "system": { "platform": "win32", "arch": "x64", "version": "Windows 10 Pro", "release": "10.0.19045", "cpuCount": 20, "cpuModel": "12th Gen Intel(R) Core(TM) i7-12700", "totalMemory": "47.75 GB", "freeMemory": "24.39 GB" }, "node": { "version": "v22.13.1", "env": "development" }, "packageManager": { "name": "npm", }, "frameworks": [ { "name": "next", "version": "16.0.6" }, { "name": "react", "version": "19.2.0" } ], "databases": null, "betterAuth": { "version": "^1.4.5", "config": null } } ``` ### Which area(s) are affected? (Select all that apply) Backend ### Auth config (if applicable) ```typescript import {betterAuth} from "better-auth" export const auth = betterAuth({ emailAndPassword: { enabled: true }, user: { deleteUser: { enabled: true }, additionalFields: { country: { type: "string", required: true } }, } }); ``` ### Additional context _No response_

GiteaMirror added the stale enhancement labels 2026-03-13 09:56:32 -05:00

GiteaMirror commented

2026-03-13 09:56:33 -05:00

@better-auth-agent[bot] commented on GitHub (Dec 5, 2025):

It looks like the custom additionalFields (like "country") aren’t being correctly picked up during TypeScript type inference for the signUpEmail call. This is similar to earlier reports where extended schema fields were not properly inferred by TS, so the API signature doesn’t accept the extra field without a workaround [1]. As a next step, you might try explicitly augmenting or casting the types for the request body in your server-side signup call. For example, adding a type assertion so that TypeScript recognizes your additional properties could work as a temporary fix, while we work on a more permanent update. Have you tried that approach, or do you have other details that might help clarify the issue further? tag @better-auth-agent if you would like an answer from the Agent

If you need more help, tag @better-auth-agent in a comment so I can respond.

Diagram • Discord • GitHub

@better-auth-agent[bot] commented on GitHub (Dec 5, 2025): It looks like the custom additionalFields (like "country") aren’t being correctly picked up during TypeScript type inference for the signUpEmail call. This is similar to earlier reports where extended schema fields were not properly inferred by TS, so the API signature doesn’t accept the extra field without a workaround [[1]](https://github.com/better-auth/better-auth/issues/6446). As a next step, you might try explicitly augmenting or casting the types for the request body in your server-side signup call. For example, adding a type assertion so that TypeScript recognizes your additional properties could work as a temporary fix, while we work on a more permanent update. Have you tried that approach, or do you have other details that might help clarify the issue further? tag @better-auth-agent if you would like an answer from the Agent _If you need more help, tag @better-auth-agent in a comment so I can respond._  [Diagram](https://repodiagrams.s3.eu-north-1.amazonaws.com/skyvern_ultra_detailed_interactive.html) • [Discord](https://discord.gg/fG2XXEuQX3) • [GitHub](https://github.com/Skyvern-AI/Skyvern) [![Diagram](https://img.shields.io/badge/Diagram-2b3137?style=flat-square)](https://repodiagrams.s3.eu-north-1.amazonaws.com/skyvern_ultra_detailed_interactive.html) [![Join](https://img.shields.io/badge/join-5865F2?logo=discord&logoColor=white&style=flat-square)](https://discord.gg/fG2XXEuQX3) [![Star](https://img.shields.io/badge/star-181717?logo=github&logoColor=white&style=flat-square)](https://github.com/Skyvern-AI/Skyvern)

GiteaMirror commented

2026-03-13 09:56:33 -05:00

@dosubot[bot] commented on GitHub (Dec 5, 2025):

Hi @GreedyPirate! I'm Dosu and I’m helping the better-auth team.

This is a known TypeScript inference limitation in Better Auth v1.4.5. Even though additionalFields like country are accepted and validated at runtime in signUpEmail, the TypeScript types for the API call do not automatically include these custom fields, so you get a TS2769 error when passing them in the body. This happens because the type definitions for signUpEmail's body don't dynamically reflect your additionalFields config, even though the runtime logic does support them (source).

Recent PRs (like #6287) have improved runtime support and API responses for additional fields, but as of now, TypeScript still requires a workaround. The recommended options are:

Use //@ts-expect-error above the body object when passing custom fields (example).

Use explicit type casting when exporting your auth instance to help with type inference:

export const auth = betterAuth(authConfig) as ReturnType<typeof betterAuth<typeof authConfig>>;

For more portable type inference, use typeof auth.$Infer.Session.user and typeof auth.$Infer.Session.session for your custom user/session types (reference).

Until the type definitions are fully improved, these workarounds are the best way to pass custom fields to signUpEmail without breaking type safety elsewhere. You can track progress and related discussions in issue #1194 and issue #5637.

To reply, just mention @dosu.

^{How did I do? Good | Irrelevant | Incorrect | Verbose | Hallucination | Report 🐛 | Other}

@dosubot[bot] commented on GitHub (Dec 5, 2025):  Hi @GreedyPirate! I'm [Dosu](https://go.dosu.dev/dosubot) and I’m helping the better-auth team.  This is a known TypeScript inference limitation in Better Auth v1.4.5. Even though additionalFields like country are accepted and validated at runtime in signUpEmail, the TypeScript types for the API call do not automatically include these custom fields, so you get a TS2769 error when passing them in the body. This happens because the type definitions for signUpEmail's body don't dynamically reflect your additionalFields config, even though the runtime logic does support them ([source](https://github.com/better-auth/better-auth/blob/be00f10cad5bbad5a0dababa4b836a3d95ce7747/packages/better-auth/src/api/routes/sign-up.ts#L14-L238)). Recent PRs (like [#6287](https://github.com/better-auth/better-auth/pull/6287)) have improved runtime support and API responses for additional fields, but as of now, TypeScript still requires a workaround. The recommended options are: - Use //@ts-expect-error above the body object when passing custom fields ([example](https://github.com/better-auth/better-auth/pull/5042)). - Use explicit type casting when exporting your auth instance to help with type inference: ```ts export const auth = betterAuth(authConfig) as ReturnType<typeof betterAuth<typeof authConfig>>; ``` - For more portable type inference, use typeof auth.$Infer.Session.user and typeof auth.$Infer.Session.session for your custom user/session types ([reference](https://github.com/better-auth/better-auth/issues/5637)). Until the type definitions are fully improved, these workarounds are the best way to pass custom fields to signUpEmail without breaking type safety elsewhere. You can track progress and related discussions in [issue #1194](https://github.com/better-auth/better-auth/issues/1194) and [issue #5637](https://github.com/better-auth/better-auth/issues/5637).  *To reply, just mention [@dosu](https://go.dosu.dev/dosubot).* --- <sup>How did I do? [Good](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=great_response) | [Irrelevant](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=irrelevant_answer) | [Incorrect](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=incorrect_sources) | [Verbose](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=too_verbose) | [Hallucination](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=hallucination) | [Report 🐛](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=bug_report) | [Other](https://app.dosu.dev/response-feedback/6fff6586-8fe8-4e60-8c29-ffc92c286336?feedback_type=other)</sup> [![Chat with Dosu](https://dosu.dev/dosu-chat-badge.svg)](https://app.dosu.dev/cdda13d9-dd27-4d31-b09a-5d8bec92de21/ask?utm_source=github) [![Open in Cursor](https://dosu.dev/dosu-in-cursor.svg)](https://cursor.com/link/prompt?text=This%20is%20a%20known%20TypeScript%20inference%20limitation%20in%20Better%20Auth%20v1.4.5.%20Even%20though%20additionalFields%20like%20country%20are%20accepted%20and%20validated%20at%20runtime%20in%20signUpEmail%2C%20the%20TypeScript%20types%20for%20the%20API%20call%20do%20not%20automatically%20include%20these%20custom%20fields%2C%20so%20you%20get%20a%20TS2769%20error%20when%20passing%20them%20in%20the%20body.%20This%20happens%20because%20the%20type%20definitions%20for%20signUpEmail%27s%20body%20don%27t%20dynamically%20reflect%20your%20additionalFields%20config%2C%20even%20though%20the%20runtime%20logic%20does%20support%20them%20%28%5Bsource%5D%28https%3A//github.com/better-auth/better-auth/blob/be00f10cad5bbad5a0dababa4b836a3d95ce7747/packages/better-auth/src/api/routes/sign-up.ts%23L14-L238%29%29.%0A%0ARecent%20PRs%20%28like%20%5B%236287%5D%28https%3A//github.com/better-auth/better-auth/pull/6287%29%29%20have%20improved%20runtime%20support%20and%20API%20responses%20for%20additional%20fields%2C%20but%20as%20of%20now%2C%20TypeScript%20still%20requires%20a%20workaround.%20The%20recommended%20options%20are%3A%0A%0A-%20Use%20//%40ts-expect-error%20above%20the%20body%20object%20when%20passing%20custom%20fields%20%28%5Bexample%5D%28https%3A//github.com/better-auth/better-auth/pull/5042%29%29.%0A-%20Use%20explicit%20type%20casting%20when%20exporting%20your%20auth%20instance%20to%20help%20with%20type%20inference%3A%0A%20%20%60%60%60ts%0A%20%20export%20const%20auth%20%3D%20betterAuth%28authConfig%29%20as%20ReturnType%3Ctypeof%20betterAuth%3Ctypeof%20authConfig%3E%3E%3B%0A%20%20%60%60%60%0A-%20For%20more%20portable%20type%20inference%2C%20use%20typeof%20auth.%24Infer.Session.user%20and%20typeof%20auth.%24Infer.Session.session%20for%20your%20custom%20user/session%20types%20%28%5Breference%5D%28https%3A//github.com/better-auth/better-auth/issues/5637%29%29.%0A%0AUntil%20the%20type%20definitions%20are%20fully%20improved%2C%20these%20workarounds%20are%20the%20best%20way%20to%20pass%20custom%20fields%20to%20signUpEmail%20without%20breaking%20type%20safety%20elsewhere.%20You%20can%20track%20progress%20and%20related%20discussions%20in%20%5Bissue%20%231194%5D%28https%3A//github.com/better-auth/better-auth/issues/1194%29%20and%20%5Bissue%20%235637%5D%28https%3A//github.com/better-auth/better-auth/issues/5637%29.) [![Join Discord](https://img.shields.io/badge/join-5865F2?logo=discord&logoColor=white&label=)](https://go.dosu.dev/discord-bot) [![Share on X](https://img.shields.io/badge/X-share-black)](https://twitter.com/intent/tweet?text=%40dosu_ai%20helped%20me%20solve%20this%20issue!&url=https%3A//github.com/better-auth/better-auth/issues/6553)

GiteaMirror commented

2026-03-13 09:56:33 -05:00

@AntonVishal commented on GitHub (Dec 6, 2025):

Hey @GreedyPirate you need to add input: true

type: "string",
required: true,
input: true,

@AntonVishal commented on GitHub (Dec 6, 2025): Hey @GreedyPirate you need to add `input: true` ``` type: "string", required: true, input: true, ```

GiteaMirror commented

2026-03-13 09:56:34 -05:00

@dosubot[bot] commented on GitHub (Mar 7, 2026):

Hi, @GreedyPirate. I'm Dosu, and I'm helping the better-auth team manage their backlog and am marking this issue as stale.

Issue Summary:

You reported a TypeScript error when passing custom fields like "country" to auth.api.signUpEmail() in Better Auth v1.4.5.
The issue stems from TypeScript types not recognizing these custom fields despite runtime support.
Maintainers confirmed this is a known TypeScript inference limitation and suggested workarounds such as type assertions, //@ts-expect-error, or explicit casting of the auth instance.
Recent PRs have improved runtime handling of additional fields, but full TypeScript type support for additionalFields is still pending.
Advice was also given to ensure custom fields include input: true in their type definitions.

Next Steps:

Please let me know if this issue is still relevant with the latest version of better-auth by commenting here.
If I don’t hear back within 7 days, this issue will be automatically closed.

Thanks for your understanding and contribution!

@dosubot[bot] commented on GitHub (Mar 7, 2026): Hi, @GreedyPirate. I'm [Dosu](https://dosu.dev), and I'm helping the better-auth team manage their backlog and am marking this issue as stale. **Issue Summary:** - You reported a TypeScript error when passing custom fields like "country" to `auth.api.signUpEmail()` in Better Auth v1.4.5. - The issue stems from TypeScript types not recognizing these custom fields despite runtime support. - Maintainers confirmed this is a known TypeScript inference limitation and suggested workarounds such as type assertions, `//@ts-expect-error`, or explicit casting of the auth instance. - Recent PRs have improved runtime handling of additional fields, but full TypeScript type support for `additionalFields` is still pending. - Advice was also given to ensure custom fields include `input: true` in their type definitions. **Next Steps:** - Please let me know if this issue is still relevant with the latest version of better-auth by commenting here. - If I don’t hear back within 7 days, this issue will be automatically closed. Thanks for your understanding and contribution!

GiteaMirror referenced this issue

2026-03-13 11:42:12 -05:00

[PR #2466] [CLOSED] chore(passkey): allow attestation type option #4335

GiteaMirror referenced this issue

2026-04-13 08:28:44 -05:00

[PR #2466] [CLOSED] chore(passkey): allow attestation type option #12582

GiteaMirror referenced this issue

2026-04-13 10:32:19 -05:00

[PR #8822] feat(passkey): allow for `attestationType: "direct"` #16483

GiteaMirror referenced this issue

2026-04-15 20:13:35 -05:00

[PR #2466] [CLOSED] chore(passkey): allow attestation type option #21236

GiteaMirror referenced this issue

2026-04-15 22:44:14 -05:00

[PR #8822] feat(passkey): allow for `attestationType: "direct"` #25137

GiteaMirror referenced this issue

2026-04-17 21:10:37 -05:00

[PR #2466] [CLOSED] chore(passkey): allow attestation type option #29936

Sign in to join this conversation.

Branches Tags

dependabot/npm_and_yarn/demo/electron/demo-minor-patch-227a091249

dependabot/github_actions/github-actions-98f3470200

2026-05-13/ci/stabilize-docker-startup

dependabot/npm_and_yarn/samlify-2.13.0

changeset-release/main

main

2026-05-22/chore/adopt-agents-md

2026-05-22/refactor/string-case-utils

2026-05-14/fix/passkey-verify-error-and-claim

changeset-release/next

client-assertions-main

2026-05-15/ci/fix-sqlite-abi-mismatch

2026-05-15/fix/organization-team-add-cascade

2026-05-15/fix/parse-set-cookie-value-validation

2026-05-13/feat/captcha-wildcard-endpoints

fix/i18n-before-hook-translation

fix/disable-migration-generate

2026-05-07/fix/admin-set-password-upsert

2026-05-10/fix/cookie-drain-order

2026-05-10/feat/hooks-finally

2026-05-09/fix/cookie-drain-order

2026-05-09/feat/hooks-finally

2026-05-08/feat/register-before-send

fix/stripe/subscription-data-merge

2026-05-01/chore/pnpm-v11-harden

chore/pnpm-v11

2026-04-29/feat/google-include-granted-scopes

2026-04-29/fix/oauth-account-scope-semantics

2026-04-27/fix/nextcookies-idempotent-writes

2026-04-26/fix/harden-proxy-host-validation

2026-04-26/refactor/stripe-callback-signature-cleanup

2026-04-26/fix/stripe-subscription-callback-timing

2026-04-11/fix/sveltekit-app-modules

feat/open-api-zod-contract

feat/oauth-provider-backchannel-logout-next

feat/oauth-idp-initiated-bounce

refactor/sign-in-challenges

2026-04-21/fix/oauth-rfc-input-validation

fix/release-notes-new-packages

fix/two-factor-identity-guard

fix/resource

feat/emailpassword-authorize

2026-04-12/security/dynamic-baseurl-proxy-trust-default

feat/oauth-provider-at-hash-v2

fix/release-grep-fallback

claude/address-review-comments-JhFLr

claude/slack-update-stripe-docs-consistency-8Sc0w

feat/async-auth

fix/two-factor-totp-verified-enrollment

feat/plugin-ui

codex/blog-1-6-release-post

2026-04-06/fix/type-any-guards

2026-04-05/chore/downgrade-better-call

2026-04-04/ci/skip-vercel-fork-prs

2026-03-28/ci/add-autofix-ci

chore/release-preview-script

himself65/2026/02/19/role

2026-03-24/fix/update-user-info-on-link

2026-03-20/docs/improve-website

2026-03-20/fix/anonymous-onlinkaccount-expo

2026-02-17/fix/anonymous-link-state

fix/8607-saml-inresponseto

fix/8549-scim-patch-noop

v1.4.x

refactor/migration-snapshot-tests

worktree-magic-link-additional-data

chore/migrate-build-to-rollup

worktree-fix-dynamic-baseurl-8447

2026-03-06/chore/public-api-check

fix/close-8156-regression-test

fix/secondary-storage-json-error-handling

himself65/verification-namespace

cursor/issue-8307-validation-79a3

himself65/2026/01/30/error-mdx

v1.4.x-staging

fix/email-otp-user

fix/restrict-full-organization-access-roles

himself65/2026/02/12/count

himself65/2026/02/04/define-plugin

2026-02-04/feat/add-pluralize

cursor/better-auth-js-integration-ec21

cursor/expo-state-mismatch-394c

2026-02-01/fix/org-update-role-sync-members

cursor/issue-7607-investigation-e146

cursor/email-generation-helper-0ff6

himself65/2026/01/21/avoid-spread-operator

himself65/2026/01/14/cli

claude/slack-add-docs-pr-NMvgO

claude/slack-add-advanced-useplural-WHKYL

feat/hooks-pos

feat/2fa-phone

feat/2fa

fix/rotation

fix/username-check

v1.3.x

refactor/organization

feat/multiple-client-ids-social-providers

1 Participants

Notifications

Due Date

No due date set.

Dependencies

No dependencies set.

Reference: github-starred/better-auth#2466