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The email signer authenticates users with a one-time password (OTP) sent to their email address. The OTP backend and the derived Stellar ed25519 key are custodied server-side by the facilitator; the browser only ever sees the public key and 64-byte signatures, delivered through your same-origin signer-proxy.

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When to use

Choose emailSigner when you want the lowest-friction onboarding: the user enters their email, receives a code, and pays - no wallet install, no seed phrase, no OAuth account. The resulting key backs a classic G... account.
The OTP backend secret and the custodied private key are never in the browser bundle. Configure a same-origin proxyUrl pointing at your backend signer-proxy, created with createSignerProxyRoute from @buckspay/nextjs. The private key never reaches client-side code.

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Factory

import { emailSigner } from "@buckspay/signers/email";

const signer = emailSigner({
  proxyUrl: "/api/buckspay/auth/email",
  network:  "testnet"
});
emailSigner(opts) accepts an EmailSignerOptions object:
OptionTypeRequiredDescription
proxyUrlstringYesSame-origin route to the @buckspay/nextjs signer-proxy
network"testnet" | "pubnet"YesStellar network to target

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Two-step authentication

The email signer uses a two-step flow before the payment: Step 1 - Request the OTP 
await signer.requestOtp(email);
// Sends the one-time code to the user's inbox.
Step 2 - Verify and authenticate 
const details = await signer.authenticate?.({ email, otp: codeFromInbox });
// details: AuthDetails { publicKey: "G...", provider: "email" }
After authenticate() resolves, the signer’s getPublicKey() and signAuthEntry() are ready and the payment can proceed with the normal prepare -> sign -> send flow.

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Server-side proxy

Mount the signer-proxy in your backend: 
// app/api/buckspay/auth/email/route.ts
import { createSignerProxyRoute } from "@buckspay/nextjs";
export const POST = createSignerProxyRoute({ provider: "email", network: "testnet" });
The proxy forwards the issue and verify actions to the facilitator with the backend secret.

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Example

// Recipe 16 - EMAIL / OTP LOGIN -> gasless USDC. Browser app.
//
// The user enters their email, receives a one-time code, and verifies it. The OTP backend
// and the derived ed25519 key are custodied by the facilitator; the browser only ever sees
// the public key + signatures, reached through YOUR signer-proxy. No secret ships client-side.
import { createBuckspayClient, createRpcSimContext, type BuckspayConfig } from "@buckspay/core";
import { classicAccount } from "@buckspay/accounts/classic";
import { emailSigner } from "@buckspay/signers/email";
import { buckspayFacilitator } from "@buckspay/relayer/buckspay-facilitator";

const USDC_SAC_TESTNET = "CBIELTK6YBZJU5UP2WWQEUCYKLPU6AUNZ2BQ4WWFEIE3USCIHMXQDAMA";
const MERCHANT = "GA6HCMBLTZS5VYYBCATRBR5VBZJEH5C2OON6XQGB3RNYDDAQ7JZ65YQH";

const signer = emailSigner({
  // YOUR same-origin signer-proxy route; forwards to the facilitator with creds server-side.
  proxyUrl: "/api/buckspay/auth/email",
  network: "testnet"
});

export const emailConfig: BuckspayConfig = {
  network: "testnet",
  account: classicAccount(),
  signer,
  relayer: buckspayFacilitator({ url: "/api/buckspay/relay", network: "testnet" }),
  gas: { mode: "sponsored" }
};

export const emailClient = createBuckspayClient(
  emailConfig,
  createRpcSimContext("https://soroban-testnet.stellar.org")
);

export async function payWithEmailLogin(email: string, otpFromInbox: string): Promise<void> {
  // 1. Issue the code (UI then collects it from the user's inbox).
  await signer.requestOtp(email);
  // 2. Verify the code -> resolves the custodied Stellar ed25519 key.
  const details = await signer.authenticate?.({ email, otp: otpFromInbox });
  console.log("signed in as", details?.publicKey, "via", details?.provider);

  // 3. Ordinary gasless payment - accounts/relayer/engine are untouched.
  await emailClient.connect();
  const call = emailClient.transfer({ token: USDC_SAC_TESTNET, to: MERCHANT, amount: "2.00" });
  const receipt = await emailClient.pay([call]);
  console.log(receipt.transferTx);
}

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Next

Social login

Use an OAuth provider (Google, Apple, Discord) instead of an email code.

Facilitator and BFF

How the signer-proxy and API key work together server-side.