BA
Better Auth•5mo ago
Nick

SyntaxError: "[object Object]" is not valid JSON on Google oauth callback

I'm trying to setup google oauth login and I'm receiving a strange error when the provider calls the callback URL. What I get in my server logs (I've added some logging in the library code): 
state o2c5WeQomqhNbjem-NPwSEbeDk3Eg_J6
data {
  identifier: 'o2c5WeQomqhNbjem-NPwSEbeDk3Eg_J6',
  value: {
    callbackURL: 'http://localhost:3000',
    codeVerifier: 'jLuPd26AbFA5HtvW9mgzMZxNN28W8sK7tciEeHdQjmN_Ifqx6oUziJnZfzLUs73gE9aDq5zIOnXziatPevZ5c18qsvHeSTa25PombgxlxuNz9J30IcrLv97SL3SeZT-O',
    expiresAt: 1748903080836,
    requestSignUp: true
  },
  expiresAt: 2025-06-02T22:24:40.836Z,
  createdAt: 2025-06-02T22:14:40.836Z,
  updatedAt: 2025-06-02T22:14:40.836Z,
  id: '6m6lvQhyPJ4SctcRINSSFoK7ijIcdD3Y'
}
# SERVER_ERROR:  SyntaxError: "[object Object]" is not valid JSON
    at JSON.parse (<anonymous>)
    at parseState (file:///Users/nick/Workspace/portal/cms-frontend/node_modules/.pnpm/better-auth@1.2.8/node_modules/better-auth/dist/shared/better-auth.dn8_oqOu.mjs:83:17)
    ...
state o2c5WeQomqhNbjem-NPwSEbeDk3Eg_J6
data {
  identifier: 'o2c5WeQomqhNbjem-NPwSEbeDk3Eg_J6',
  value: {
    callbackURL: 'http://localhost:3000',
    codeVerifier: 'jLuPd26AbFA5HtvW9mgzMZxNN28W8sK7tciEeHdQjmN_Ifqx6oUziJnZfzLUs73gE9aDq5zIOnXziatPevZ5c18qsvHeSTa25PombgxlxuNz9J30IcrLv97SL3SeZT-O',
    expiresAt: 1748903080836,
    requestSignUp: true
  },
  expiresAt: 2025-06-02T22:24:40.836Z,
  createdAt: 2025-06-02T22:14:40.836Z,
  updatedAt: 2025-06-02T22:14:40.836Z,
  id: '6m6lvQhyPJ4SctcRINSSFoK7ijIcdD3Y'
}
# SERVER_ERROR:  SyntaxError: "[object Object]" is not valid JSON
    at JSON.parse (<anonymous>)
    at parseState (file:///Users/nick/Workspace/portal/cms-frontend/node_modules/.pnpm/better-auth@1.2.8/node_modules/better-auth/dist/shared/better-auth.dn8_oqOu.mjs:83:17)
    ...
the library code at the top of the stack is this function: 
async function parseState(c) {
  const state = c.query.state || c.body.state;
  const data = await c.context.internalAdapter.findVerificationValue(state);
  console.log("state", state);
  console.log("data", data);
  if (!data) {
    c.context.logger.error("State Mismatch. Verification not found", {
      state
    });
    throw c.redirect(
      `${c.context.baseURL}/error?error=please_restart_the_process`
    );
  }
  const parsedData = z.object({
     ....
  }).parse(JSON.parse(data.value));
  ...
}
async function parseState(c) {
  const state = c.query.state || c.body.state;
  const data = await c.context.internalAdapter.findVerificationValue(state);
  console.log("state", state);
  console.log("data", data);
  if (!data) {
    c.context.logger.error("State Mismatch. Verification not found", {
      state
    });
    throw c.redirect(
      `${c.context.baseURL}/error?error=please_restart_the_process`
    );
  }
  const parsedData = z.object({
     ....
  }).parse(JSON.parse(data.value));
  ...
}
when I remove the JSON.parse call in that function I am able to complete the oauth sign in sucessfully. Info about my environment: better-auth 1.2.8 (had the same issue on 1.2.7 and tried upgrading) hono 4.7.8 Is this a bug in the library or in my setup? Confused how the library expects a json string there but its already an object. Thanks in advance!
Solution:
Sorry, this was a problem on my side. I had the kysely plugin ParseJSONResultsPlugin enabled on the adapter
Jump to solution
5 Replies
Nick
NickOP•5mo ago
auth config: 
import { betterAuth } from "better-auth";
import { captcha, emailOTP } from "better-auth/plugins";

import { kysely } from "@lib/database/kysely";

import { sendSignInOTPEmail, sendVerificationEmail } from "./authn/emails";

export const auth = betterAuth({
  trustedOrigins: ["*"],
  database: {
    db: kysely,
    type: "postgres",
    casing: "snake",
  },
  socialProviders: {
    google: {
      prompt: "select_account",
      clientId: process.env.GOOGLE_OAUTH_CLIENT_ID!,
      clientSecret: process.env.GOOGLE_OAUTH_CLIENT_SECRET!,
    },
  },
  emailAndPassword: {
    enabled: true,
  },
  emailVerification: {
    sendVerificationEmail: async ({ user, url }, _request) => {
      await sendVerificationEmail(user.email, url);
    },
    sendOnSignUp: true,
  },
  plugins: [
    emailOTP({
      async sendVerificationOTP({ email, otp }, _request) {
        await sendSignInOTPEmail(email, otp);
      },
    }),
    captcha({
      provider: "cloudflare-turnstile",
      secretKey: process.env.TURNSTILE_SECRET_KEY!,
    }),
  ],
  advanced: {
    cookiePrefix: "portal-authn",
  },
  user: {
    modelName: "authn_users",
  },
  session: {
    modelName: "authn_sessions",
  },
  account: {
    modelName: "authn_accounts",
  },
  verification: {
    modelName: "authn_verifications",
  },
});
import { betterAuth } from "better-auth";
import { captcha, emailOTP } from "better-auth/plugins";

import { kysely } from "@lib/database/kysely";

import { sendSignInOTPEmail, sendVerificationEmail } from "./authn/emails";

export const auth = betterAuth({
  trustedOrigins: ["*"],
  database: {
    db: kysely,
    type: "postgres",
    casing: "snake",
  },
  socialProviders: {
    google: {
      prompt: "select_account",
      clientId: process.env.GOOGLE_OAUTH_CLIENT_ID!,
      clientSecret: process.env.GOOGLE_OAUTH_CLIENT_SECRET!,
    },
  },
  emailAndPassword: {
    enabled: true,
  },
  emailVerification: {
    sendVerificationEmail: async ({ user, url }, _request) => {
      await sendVerificationEmail(user.email, url);
    },
    sendOnSignUp: true,
  },
  plugins: [
    emailOTP({
      async sendVerificationOTP({ email, otp }, _request) {
        await sendSignInOTPEmail(email, otp);
      },
    }),
    captcha({
      provider: "cloudflare-turnstile",
      secretKey: process.env.TURNSTILE_SECRET_KEY!,
    }),
  ],
  advanced: {
    cookiePrefix: "portal-authn",
  },
  user: {
    modelName: "authn_users",
  },
  session: {
    modelName: "authn_sessions",
  },
  account: {
    modelName: "authn_accounts",
  },
  verification: {
    modelName: "authn_verifications",
  },
});
the callsite: 
  const handleSignInWithGoogle = async () => {
    try {
      const response = await authClient.signIn.social({ provider: "google", requestSignUp: true, fetchOptions: { headers: { "x-captcha-response": formState.turnstileToken } } });
      console.log(response);
    } catch (error) {
      console.error("Error during form submission:", error);
      setAuthError(error instanceof Error ? error.message : "An unexpected error occurred");
    }
  };
  const handleSignInWithGoogle = async () => {
    try {
      const response = await authClient.signIn.social({ provider: "google", requestSignUp: true, fetchOptions: { headers: { "x-captcha-response": formState.turnstileToken } } });
      console.log(response);
    } catch (error) {
      console.error("Error during form submission:", error);
      setAuthError(error instanceof Error ? error.message : "An unexpected error occurred");
    }
  };
Solution
Nick
Nick•4mo ago
Sorry, this was a problem on my side. I had the kysely plugin ParseJSONResultsPlugin enabled on the adapter
andreasb
andreasb•4mo ago
@Nick How did you end up dealing with this? Not having ParseJSONResultsPlugin will cause all sorts of issue with non-Better Auth queries, but leaving it in causes the "[object Object]" issue.
Nick
NickOP•4mo ago
@andreasb My app didn't need ParseJSONResultsPlugin so I just removed it, I added it accidentally while migrating from supabase-js to kysely for a SSR app. Sorry that's not a great answer, maybe you could consider removing it and manually doing the JSON parsing yourself with a library like zod Another idea could be to create a different db adapter for better-auth than your primary app
andreasb
andreasb•4mo ago
@Nick Thank you! Both very good suggestions, very much appreciated! I also see that ParseJSONResultsPlugin can be added on a per-query basis, but the dual db adapter approach must be tried, sounds a lot easier. For future reference, ended up with a variant of Nick's suggestion: 
export const betterAuthDBClient = kyselyClient.withoutPlugins();
export const betterAuthDBClient = kyselyClient.withoutPlugins();
Had no idea withoutPlugins() was a thing, solved it immediately!

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