📲Sign in With X

This functionality is currently only supported on EVM networks and is 100% compliant with EIP-4361 (Sign in With Ethereum). We will be adding support for more networks soon.

To verify a customer's externally-owned account ownership, we require a challenge to be signed with the private key. This mechanism is outlined in CAIP-122, originally known as "Sign in With Ethereum" (SIWE) but expanded to support other blockchains. When a new customer object is created in our system, we generate a challenge following the standardised structure, expecting it to be signed and verified before proceeding with user onboarding. The challenge returned by the endpoint is a Base64-encoded string.

Create new customer

post

https://api.offblocks.xyz/v1https://api.sandbox.offblocks.xyz/v1

/customers

Creates new customer and generates a cryptographic challenge to verify ownership of blockchain account

Authorizations

bearerAuth

AuthorizationstringRequired

Bearer authentication header of the form Bearer <token>.

Header parameters

SignaturestringRequired

HTTP message signature

Signature-InputstringRequired

HTTP message signature input

Idempotency-Keystring · uuidRequired

Idempotency key (UUID)

Content-DigeststringRequired

Content digest

Body

application/json

chainIdstringRequired

Unique customer ID in a form of a valid on-chain address. This would normally correspond to customer's EOA wallet address

Example: eip155:1:0xab16a96D359eC26a11e2C2b3d8f8B8942d5Bfcdb

externalIdstringRequired

Unique customer ID in a form of an external identifier. This would normally correspond to customer's ID in your system

Responses

201

Successful operation

application/json

400

Invalid request

401

Not authorised

409

Customer already exists

500

Internal error

post

/customers

HTTPcURLJavaScriptPython

POST /v1/customers HTTP/1.1
Host: api.offblocks.xyz
Authorization: Bearer YOUR_SECRET_TOKEN
Signature: text
Signature-Input: text
Idempotency-Key: 123e4567-e89b-12d3-a456-426614174000
Content-Digest: text
Content-Type: application/json
Accept: */*
Content-Length: 85

{
  "chainId": "eip155:1:0xab16a96D359eC26a11e2C2b3d8f8B8942d5Bfcdb",
  "externalId": "text"
}

{
  "id": "123e4567-e89b-12d3-a456-426614174000",
  "externalId": "text",
  "chainId": "eip155:1:0xab16a96D359eC26a11e2C2b3d8f8B8942d5Bfcdb",
  "status": "initiating",
  "createdAt": "2025-12-15T18:55:39.539Z",
  "updatedAt": "2025-12-15T18:55:39.539Z",
  "challenge": "LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUZZd0VBWUhLb1pJemowQ0FRWUZLNEVFQUFvRFFnQUUzTEw1RldmVFgvL3BJaXNEL0xneFVIT2lxdlFTSUVWTgpGekloOTdLZXBlWk1iZVZsUGd1akZ4Yk5MN2x1ZVhRQnBpUWUzNmZLN0xSbXZNNHdEaWZFTkE9PQotLS0tLUVORCBQVUJMSUMgS0VZLS0tLS0="
}

When a new user is created on supported chains, you will receive a Base64 encoded challenge, which resembles the following:

api.sandbox.offblocks.xyz wants you to sign in with your Ethereum account:
0x43158f45b5EbD7b1179130130DF00393928C2691

OffBlocks wants to verify ownership of your wallet. By connecting your wallet and using OffBlocks, you agree to our Terms of services and Privacy Policy

URI: https://api.sandbox.offblocks.xyz
Version: 1
Chain ID: 300
Nonce: 5ufoiEqDaFvmfo78
Issued At: 2024-01-17T18:21:53Z

In order to proceed with ownership verification, your customer needs to sign this challenge with their private key. Please, follow SIWE documentation to learn more about signing SIWE challenges using community supported libraries. For testing purposes, you can use MyCrypto signing tools to sign a challenge for test accounts.

If everything was successful, you will have a HEX-formatted signature ready to be submitted to our API. For example, if using MyCrypto, it will produce a following message for the above challenge:

{
  "address": "0x43158f45b5EbD7b1179130130DF00393928C2691",
  "msg": "api.sandbox.offblocks.xyz wants you to sign in with your Ethereum account:\n0x43158f45b5EbD7b1179130130DF00393928C2691\n\nOffBlocks wants to verify ownership of your wallet. By connecting your wallet and using OffBlocks, you agree to our Terms of services and Privacy Policy\n\nURI: https://api.sandbox.offblocks.xyz\nVersion: 1\nChain ID: 300\nNonce: 5ufoiEqDaFvmfo78\nIssued At: 2024-01-17T18:21:53Z",
  "sig": "0xd2472857a11a29b612fda39b3a381cc88a8e6d085333cb7e2536ea38e71664be5e88ada8f5de966eff4f7c9cf59429b9a24814d878e779db34b612d4091c26ba1c",
  "version": "2"
}

To submit a signed challenge, please encode a HEX signature as Base64 string and send it using the corresponding endpoint.

Sign previously issued customer challenge

post

https://api.offblocks.xyz/v1https://api.sandbox.offblocks.xyz/v1

/customers/{customerId}/challenge/sign

Signs previously issued challenge to verify customer's ownership of their blockchain account

Authorizations

bearerAuth

AuthorizationstringRequired

Bearer authentication header of the form Bearer <token>.

Path parameters

customerIdstring · uuidRequired

Unique customer ID

Header parameters

SignaturestringRequired

HTTP message signature

Signature-InputstringRequired

HTTP message signature input

Idempotency-Keystring · uuidRequired

Idempotency key (UUID)

Content-DigeststringRequired

Content digest

Body

application/json

Cryptographic signature generated using owner's EOA private key according to chain-specific algorithm. Signature is used for signing on-chain transactions such as creating a new account, authorising a recurring payment or setting up spending limits

ownerIdstringRequired

Unique signer account ID in a form of a valid on-chain address

Example: eip155:1:0xab16a96D359eC26a11e2C2b3d8f8B8942d5Bfcdb

challengestring · byteRequired

Original base64 encoded challenge provided by this API for owner to sign

Example: LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUZZd0VBWUhLb1pJemowQ0FRWUZLNEVFQUFvRFFnQUUzTEw1RldmVFgvL3BJaXNEL0xneFVIT2lxdlFTSUVWTgpGekloOTdLZXBlWk1iZVZsUGd1akZ4Yk5MN2x1ZVhRQnBpUWUzNmZLN0xSbXZNNHdEaWZFTkE9PQotLS0tLUVORCBQVUJMSUMgS0VZLS0tLS0=

signaturestring · byteRequired

Base64 encoded signature

Example: IfvwaW1eCqLvQaK0/7YjvK8HBGHWHPclHHQWH4L+w6Q3CFS8CjSzq0h8G8AhzTGMc0xRrik3TyvrDm8t1JtL9Bw=

Responses

204

Successful operation

400

Invalid request

401

Not authorised

404

Customer not found

409

Challenge already signed

500

Internal error

post

/customers/{customerId}/challenge/sign

HTTPcURLJavaScriptPython

POST /v1/customers/{customerId}/challenge/sign HTTP/1.1
Host: api.offblocks.xyz
Authorization: Bearer YOUR_SECRET_TOKEN
Signature: text
Signature-Input: text
Idempotency-Key: 123e4567-e89b-12d3-a456-426614174000
Content-Digest: text
Content-Type: application/json
Accept: */*
Content-Length: 415

{
  "ownerId": "eip155:1:0xab16a96D359eC26a11e2C2b3d8f8B8942d5Bfcdb",
  "challenge": "LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUZZd0VBWUhLb1pJemowQ0FRWUZLNEVFQUFvRFFnQUUzTEw1RldmVFgvL3BJaXNEL0xneFVIT2lxdlFTSUVWTgpGekloOTdLZXBlWk1iZVZsUGd1akZ4Yk5MN2x1ZVhRQnBpUWUzNmZLN0xSbXZNNHdEaWZFTkE9PQotLS0tLUVORCBQVUJMSUMgS0VZLS0tLS0=",
  "signature": "IfvwaW1eCqLvQaK0/7YjvK8HBGHWHPclHHQWH4L+w6Q3CFS8CjSzq0h8G8AhzTGMc0xRrik3TyvrDm8t1JtL9Bw="
}

No content

If, for any reason, the original challenge is lost or cannot be signed immediately, you can fetch it again using a dedicated endpoint. If we encounter an error during signature validation via /sign endpoint, a new challenge will be issued for you to retrieve.

We enforce a 1 hour expiration window via our API for all issued challenges for security purposes. If a challenge hasn't been signed within 1 hour from issue, we will generate a new one and make it available through this endpoint.

Retrieve customer challenge

get

https://api.offblocks.xyz/v1https://api.sandbox.offblocks.xyz/v1

/customers/{customerId}/challenge

Retrieves challenge to verify customer's ownership of their blockchain account

Authorizations

bearerAuth

AuthorizationstringRequired

Bearer authentication header of the form Bearer <token>.

Path parameters

customerIdstring · uuidRequired

Unique customer ID

Header parameters

SignaturestringRequired

HTTP message signature

Signature-InputstringRequired

HTTP message signature input

Responses

200

Successful operation

application/json

400

Invalid request

401

Not authorised

404

Customer not found

500

Internal error

get

/customers/{customerId}/challenge

HTTPcURLJavaScriptPython

GET /v1/customers/{customerId}/challenge HTTP/1.1
Host: api.offblocks.xyz
Authorization: Bearer YOUR_SECRET_TOKEN
Signature: text
Signature-Input: text
Accept: */*

{
  "challenge": "LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUZZd0VBWUhLb1pJemowQ0FRWUZLNEVFQUFvRFFnQUUzTEw1RldmVFgvL3BJaXNEL0xneFVIT2lxdlFTSUVWTgpGekloOTdLZXBlWk1iZVZsUGd1akZ4Yk5MN2x1ZVhRQnBpUWUzNmZLN0xSbXZNNHdEaWZFTkE9PQotLS0tLUVORCBQVUJMSUMgS0VZLS0tLS0="
}