Preamble

SEP: 0038
Title: Anchor RFQ API
Author: Jake Urban <@jakeurban> and Leigh McCulloch <@leighmcculloch>
Track: Standard
Status: Draft
Created: 2021-04-09
Updated: 2022-05-23
Discussion: https://github.com/stellar/stellar-protocol/issues/901
Version 2.0.0

Summary

This protocol enables anchors to accept off-chain assets in exchange for different on-chain assets, and vice versa. Specifically, it enables anchors to provide quotes that can be referenced within the context of existing Stellar Ecosystem Proposals. How the exchange of assets is facilitated is outside the scope of this document.

Motivation

Anchoring an asset and issuing an asset are distinct functions that have different business and technical requirements. However, issuing an asset has often been a prerequisite for anchoring an asset. This protocol enables anchors to transfer value on and off the Stellar network for their clients regardless of whether a one-for-one reserve-backed Stellar asset exists for the off-chain asset held by the anchor's clients.

Removing this requirement for anchors also provides downstream benefits to ecosystem participants generally. Enabling anchors to accept any Stellar asset will naturally decrease liquidity fragmentation on the decentralized exchange, leading to greater market depth and tighter spreads between trading pairs.

Specification

stellar.toml

An anchor must define the location of their ANCHOR_QUOTE_SERVER in their stellar.toml. This is how a wallet knows where to find the anchor's server.

Authentication

This protocol's endpoints use authentication in the form of a SEP-10 JSON Web Token (JWT) in the Authorization header of the request.

Authentication is mandatory for POST /quote and GET /quote/:id, but optional for the remaining endpoints. When optional, if authentication is provided it can be used to personalize the respective responses.

Authorization: Bearer <jwt>

Content Type

All endpoints accept in requests the following Content-Type:

application/json

All endpoints respond with content type:

application/json

Errors

If an error occurs when calling any endpoint, an appropriate HTTP status code will be returned along with an error response.

Status Code

Common HTTP status codes may be returned for a server. In particular the following are expected:

Status Code	Name	Reason
`400`	Bad Request	The request is invalid in any way.
`403`	Permission Denied	No `Authorization` header has been provided or the contents of the header are not accepted as valid.

The response body must contain a human-readable description of the reason for error:

{
  "error": "The requested asset is not supported. See GET /prices for supported assets."
}

Asset Identification Format

This protocol can be used to provide quotes for any class of asset in exchange for a Stellar asset. The following format is used to identify an asset in API requests and responses.

<scheme>:<identifer>

The currently accepted scheme values are:

Name	Description
`stellar`	Used for Stellar assets.
`iso4217`	Used for fiat currencies.

stellar Identifier Format

The SEP-11 asset format.

iso4217 Identifier Format

The ISO 4217 three-character currency code for the fiat currency.

For example, Stellar USDC would be identified as:

stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN

Fiat USD would be identified as:

iso4217:USD

Endpoints

GET /info
GET /prices
GET /price
POST /quote
GET /quote/:id

GET Info

This endpoint describes the supported Stellar assets and off-chain assets available for trading. Note that the anchor may not support a trading pair between every Stellar asset and off-chain asset listed. Use the GET /prices endpoint to see which pairs are supported.

Authentication

Optional SEP-10. If authentication is provided it can be used to personalize the response.

Request

No request arguments required.

Response

A 200 Success status code should be returned for successful requests.

Name	Type	Description
`assets`	array	An array of objects describing the assets available in exchange for one or more of the other assets listed.

assets Object Schema

Name	Type	Description
`asset`	string	The Asset Identification Format value.
`sell_delivery_methods`	array	(optional) Only for non-Stellar assets. An array of objects describing the methods a client can use to sell/deliver funds to the anchor. The method of delivery may affect the expiration and/or price provided in a `POST /quote` response. If the delivery method is not necessary for providing accurate quotes and expirations, the server can omit this attribute.
`buy_delivery_methods`	array	(optional) Only for non-Stellar assets. An array of objects describing the methods a client can use to buy/retrieve funds from the anchor. The method of delivery may affect the expiration and/or price provided in a `POST /quote` response. If the delivery method is not necessary for providing accurate quotes and expirations, the server can omit this attribute.
`country_codes`	array	(optional) Only for fiat assets. A list of ISO 3166-1 alpha-3 codes of the countries where the Anchor operates for fiat transactions.

Object Schema for sell_delivery_methods and buy_delivery_methods.

Name	Type	Description
`name`	string	The value to use when making `POST /quote` requests.
`description`	string	A human readable description of the method identified by `name`.

Example

GET /info

{
  "assets":  [
    {
      "asset": "stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN"
    },
    {
      "asset": "stellar:BRL:GDVKY2GU2DRXWTBEYJJWSFXIGBZV6AZNBVVSUHEPZI54LIS6BA7DVVSP"
    },
    {
      "asset": "iso4217:BRL",
      "country_codes": ["BRA"],
      "sell_delivery_methods": [
        {
          "name": "cash",
          "description": "Deposit cash BRL at one of our agent locations."
        },
        {
          "name": "ACH",
          "description": "Send BRL directly to the Anchor's bank account."
        },
        {
          "name": "PIX",
          "description": "Send BRL directly to the Anchor's bank account."
        }
      ],
      "buy_delivery_methods": [
        {
          "name": "cash",
          "description": "Pick up cash BRL at one of our payout locations."
        },
        {
          "name": "ACH",
          "description": "Have BRL sent directly to your bank account."
        },
        {
          "name": "PIX",
          "description": "Have BRL sent directly to the account of your choice."
        }
      ]
    }
  ]
}

GET Prices

This endpoint can be used to fetch the indicative prices of available off-chain assets in exchange for a Stellar asset and vice versa.

These prices are indicative. The actual price will be calculated at conversion time once the Anchor receives the funds from a User.

The prices returned include any margin that the provider may keep as a service fee, and this margin may vary depending on the directional flow of funds, amount, delivery method, country code, or other factors.

Authentication

Optional SEP-10. If authentication is provided it can be used to personalize the response.

Request

Name	Type	Description
`sell_asset`	string	The asset you want to sell, using the Asset Identification Format.
`sell_amount`	string	The amount of `sell_asset` the client would exchange for each of the `buy_assets`.
`sell_delivery_method`	string	(optional) One of the `name` values specified by the `sell_delivery_methods` array for the associated asset returned from `GET /info`. Can be provided if the user is delivering an off-chain asset to the anchor but is not strictly required.
`buy_delivery_method`	string	(optional) One of the `name` values specified by the `buy_delivery_methods` array for the associated asset returned from `GET /info`. Can be provided if the user intends to receive an off-chain asset from the anchor but is not strictly required.
`country_code`	string	(optional) The ISO 3166-1 alpha-3 code of the user's current address. Should be provided if there are two or more country codes available for the desired asset in `GET /info`.

Response

A 200 Success status code should be returned for successful requests.

Name	Type	Description
`buy_assets`	array	An array of objects containing information on the assets that the client will receive when they provide `sell_asset`.

buy_assets Object Schema

Name	Type	Description
`asset`	string	The Asset Identification Format value.
`price`	string	The price offered by the anchor for one unit of `asset` in terms of `sell_asset`. In traditional finance, `asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`decimals`	integer	The number of decimals needed to represent `asset`.

Examples

GET /prices?sell_asset=stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&sell_amount=100&country_code=BRA&buy_delivery_method=ACH

{
  "buy_assets": [
    {
      "asset": "iso4217:BRL",
      "price": "0.18",
      "decimals": 2
    }
  ]
}

GET /prices?sell_asset=iso4217:BRL&sell_amount=500&country_code=BRA&sell_delivery_method=PIX

{
  "buy_assets": [
    {
      "asset": "stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN",
      "price": "5.42",
      "decimals": 7
    }
  ]
}

GET Price

This endpoint can be used to fetch the indicative price for a given asset pair.

The client must provide either sell_amount or buy_amount, but not both.

These prices are indicative. The actual price will be calculated at conversion time once the Anchor receives the funds from a User.

Fees can be collected by adding a margin to the price, and/or by deducting an amount from the funds provided by or delivered to the client. Both the margin and the fees may vary depending on the directional flow of funds, amount, delivery method, country code, context or other factors.

Authentication

Optional SEP-10. If authentication is provided it can be used to personalize the response.

Request

Name	Type	Description
`sell_asset`	string	The asset the client would like to sell. Ex. `USDC:G...`, `iso4217:ARS`
`buy_asset`	string	The asset the client would like to exchange for `sell_asset`.
`sell_amount`	string	The amount of `sell_asset` the client would like to exchange for `buy_asset`.
`buy_amount`	string	The amount of `buy_asset` the client would like to purchase with `sell_asset`.
`sell_delivery_method`	string	(optional) One of the `name` values specified by the `sell_delivery_methods` array for the associated asset returned from `GET /info`. Can be provided if the user is delivering an off-chain asset to the anchor but is not strictly required.
`buy_delivery_method`	string	(optional) One of the `name` values specified by the `buy_delivery_methods` array for the associated asset returned from `GET /info`. Can be provided if the user intends to receive an off-chain asset from the anchor but is not strictly required.
`country_code`	string	(optional) The ISO 3166-1 alpha-3 code of the user's current address. Should be provided if there are two or more country codes available for the desired asset in `GET /info`.
`context`	string	The context for what this quote will be used for. Must be one of `sep6` or `sep31`.

Response

A 200 Success status code should be returned for successful requests.

Name	Type	Description
`total_price`	string	The total conversion price offered by the anchor for one unit of `buy_asset` in terms of `sell_asset`, including fees. In traditional finance, `buy_asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`price`	string	The conversion price offered by the anchor for one unit of `buy_asset` in terms of `sell_asset`, without including fees. In traditional finance, `buy_asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`sell_amount`	string	The amount of `sell_asset` the anchor will exchange for `buy_asset`. It could be different from the `sell_amount` provided in the request, depending on how fees are applied by the Anchor.
`buy_amount`	string	The amount of `buy_asset` the anchor will provide with `sell_asset`. It could be different from the `buy_amount` provided in the request, depending on how fees are applied by the Anchor.
`fee`	object	An object describing the fee used to calculate the conversion price. This can be used to datail the price components for the end-user.

To better understand the relation between the *price, *amount and fee fields, please refer to the Price Formulas section.

Object Schema for fee:

Name	Type	Description
`total`	string	The total amount of fee applied.
`asset`	string	The asset in which the fee is applied, represented through the Asset Identification Format.
`details`	array	(optional) An array of objects detailing the fees that were used to calculate the conversion price. This can be used to datail the price components for the end-user.

Object Schema for fee.details:

Name	Type	Description
`name`	string	The name of the fee, for example `ACH fee`, `Brazilian conciliation fee`, `Service fee`, etc.
`description`	string	(optional) A text describing the fee.
`amount`	string	The amount of asset applied. If `fee.details` is provided, `sum(fee.details.amount)` should be equals `fee.total`.

Examples

GET /price?sell_asset=iso4217:BRL&buy_asset=stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&sell_amount=500&sell_delivery_method=PIX&country_code=BRA&context=sep6

{
  "total_price": "5.42",  // 542/100
  "price": "5.00",        // (542-42)/100
  "sell_amount": "542",
  "buy_amount": "100",
  "fee": {
    "total": "42.00",
    "asset": "iso4217:BRL"
  }
}

GET /price?sell_asset=iso4217:BRL&buy_asset=stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&buy_amount=100&sell_delivery_method=PIX&country_code=BRA&context=sep31

{
  "total_price": "5.42",      // 542/100
  "price": "5.00",            // 542/(100+8.40)
  "sell_amount": "542",
  "buy_amount": "100",
  "fee": {
    "total": "8.40",
    "asset": "stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN",
    "details": [
      {
        "name": "Service fee",
        "amount": "8.40"
      }
    ]
  }
}

GET /price?sell_asset=stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&buy_asset=iso4217:BRL&sell_amount=90&buy_delivery_method=PIX&country_code=BRA&context=sep6

{
  "total_price": "0.20",      // 100/500
  "price": "0.18",            // 100/(500+55.5556)
  "sell_amount": "100",
  "buy_amount": "500",
  "fee": {
    "total": "55.5556",
    "asset": "iso4217:BRL",
    "details": [
      {
        "name": "PIX fee",
        "description": "Fee charged in order to process the outgoing PIX transaction.",
        "amount": "55.5556"
      }
    ]
  }
}

GET /price?sell_asset=stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&buy_asset=iso4217:BRL&buy_amount=500&buy_delivery_method=PIX&country_code=BRA&context=sep31

{
  "total_price": "0.20",  // 100/500
  "price": "0.18",        // (100-10)/500
  "sell_amount": "100",
  "buy_amount": "500",
  "fee": {
    "total": "10.00",
    "asset": "stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN",
    "details": [
      {
        "name": "Service fee",
        "amount": "5.00"
      },
      {
        "name": "PIX fee",
        "description": "Fee charged in order to process the outgoing BRL PIX transaction.",
        "amount": "5.00"
      }
    ]
  }
}

Price Formulas

The following should hold true for all prices and quotes returned in the SEP-38 responses.

sell_amount = total_price * buy_amount

sell_amount - fee = price * buy_amount    // when `fee` is in `sell_asset`

- or -

sell_amount = price * (buy_amount + fee)  // when `fee` is in `buy_asset`

POST Quote

This endpoint can be used to request a firm quote for a Stellar asset and off-chain asset pair.

In contrast with the GET /price and GET /prices endpoints, the amount requested must be held in reserve and not used in calculations of subsequent quotes until the expiration provided in the response.

Protecting Against Bad Actors

To protect against bad actor clients reserving all available capital without following through with the requested trades, servers should only accept requests for quotes from Stellar accounts that belong to entities or individuals that have been properly KYC'ed, either via SEP-12 or some other mechanism.

Servers may deny access to the API if misuse is detected.

Transaction Fees

Fees can be collected by adding a margin to the price, and/or by deducting an amount from the funds provided by or delivered to the client. Both the margin and the fees may vary depending on the directional flow of funds, amount, delivery method, country code, context or other factors.

If the client requests some amount of an off-chain asset for providing some amount of a Stellar asset, the client will submit a Stellar transaction delievering funds to the anchor before the expiration included in the response, paying a fee as determined by state of the Stellar network.

In the reverse scenario, the anchor will submit a Stellar transaction to deliver funds to the client as long as the client delivered off-chain funds to the anchor before the expiration. In this case, the anchor will likely increase their margin to cover the cost of submitting the transaction.

Authentication

SEP-10.

Request

The client must provide either sell_amount or buy_amount, but not both.

Unless the list included in the GET /info response is empty or missing for the associated off-chain asset, the client must also provide either sell_delivery_method or buy_delivery_method, but not both.

Name	Type	Description
`sell_asset`	string	Same as the definition of `sell_asset` in `GET /price`.
`buy_asset`	string	Same as the definition of `buy_asset` in `GET /price`.
`sell_amount`	string	Same as the definition of `sell_amount` in `GET /price`.
`buy_amount`	string	The same definition of `buy_amount` in `GET /price`.
`expire_after`	UTC ISO 8601 string	(optional) The client's desired `expires_at` date and time for the quote. Anchors may choose an `expires_at` that occurs after the `expire_after`. Anchors should return `400 Bad Request` if the an expiration on or after the requested value cannot be provided.
`sell_delivery_method`	string	(optional) One of the `name` values specified by the `sell_delivery_methods` array for the associated asset returned from `GET /info`. Must be provided if the user is delivering an off-chain asset to the anchor unless no more than one method is specified in the `GET /info` response.
`buy_delivery_method`	string	(optional) One of the `name` values specified by the `buy_delivery_methods` array for the associated asset returned from `GET /info`. Must be provided if the user intends to receive an off-chain asset from the anchor unless no more than one method is specified in the `GET /info` response.
`country_code`	string	(optional) The ISO 3166-1 alpha-3 code of the user's current address. Should be provided if there are two or more country codes available for the desired asset in `GET /info`.
`context`	string	The context for what this quote will be used for. Must be one of `sep6` or `sep31`.

Response

A 201 Created status code should be returned for successful requests.

Name	Type	Description
`id`	string	The unique identifier for the quote to be used in other Stellar Ecosystem Proposals (SEPs).
`expires_at`	UTC ISO 8601 string	The date and time by which the anchor must receive funds from the client.
`total_price`	string	The total conversion price offered by the anchor for one unit of `buy_asset` in terms of `sell_asset`, including fees. In traditional finance, `buy_asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`price`	string	The conversion price offered by the anchor for one unit of `buy_asset` in terms of `sell_asset`, without including fees. In traditional finance, `buy_asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`sell_asset`	string	The asset the client would like to sell. Ex. `USDC:G...`, `iso4217:ARS`
`sell_amount`	string	The amount of `sell_asset` to be exchanged for `buy_asset`. It could be different from the `sell_amount` provided in the request, depending on how fees are applied by the Anchor.
`buy_asset`	string	The asset the client would like to exchange for `sell_asset`.
`buy_amount`	string	The amount of `buy_asset` to be exchanged for `sell_asset`. It could be different from the `buy_amount` provided in the request, depending on how fees are applied by the Anchor. `price * buy_amount = sell_amount` must be true up to the number of decimals required for `buy_asset`.
`fee`	object	An object describing the fee used to calculate the conversion price. This can be used to datail the price components for the end-user.

To better understand the relation between the *price, *amount and fee fields, please refer to the Price Formulas section.

GET Quote

This endpoint can be used to fetch a previously-provided firm quote. Quotes referenced in other protocols must be available at this endpoint past the expires_at expiration for the quote.

Authentication

SEP-10.

Request

Name	Type	Description
`id`	string	The unique identifier for the quote. Same as the `id` returned in the `POST /quote` response.

Response

This response body should match the response from POST /quote.

Name	Type	Description
`id`	string	The `id` specified in the request.
`expires_at`	UTC ISO 8601 string	The date and time by which the anchor must receive funds from the client.
`price`	string	The price offered by the anchor for one unit of `buy_asset` in terms of `sell_asset`. In traditional finance, `buy_asset` would be referred to as the base asset and `sell_asset` as the counter asset.
`sell_asset`	string	The asset the client would like to sell. Ex. `USDC:G...`, `iso4217:ARS`
`sell_amount`	string	The amount of `sell_asset` to be exchanged for `buy_asset`.
`buy_asset`	string	The asset the client would like to exchange for `sell_asset`.
`buy_amount`	string	The amount of `buy_asset` to be exchanged for `sell_asset`. `price * buy_amount = sell_amount` must be true up to the number of decimals required for `buy_asset`.
`fee`	object	An object describing the fee used to calculate the conversion price. This can be used to datail the price components for the end-user.

Example

GET /quote/de762cda-a193-4961-861e-57b31fed6eb3

{
  "id": "de762cda-a193-4961-861e-57b31fed6eb3",
  "expires_at": "2021-04-30T07:42:23",
  "total_price": "5.42",        // 542/100
  "price": "5.00",              // (542-42)/100
  "sell_asset": "iso4217:BRL",
  "sell_amount": "542",
  "buy_asset": "stellar:USDC:GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN&",
  "buy_amount": "100",
  "fee": {
    "total": "42.00",
    "asset": "iso4217:BRL",
    "details": [
      {
        "name": "PIX fee",
        "description": "Fee charged in order to process the outgoing PIX transaction.",
        "amount": "12.00"
      },
      {
        "name": "Brazilian conciliation fee",
        "description": "Fee charged in order to process conciliation costs with intermediary banks.",
        "amount": "15.00"
      },
      {
        "name": "Service fee",
        "amount": "15.00"
      }
    ]
  }
}

Changelog

v2.0.0: (i) add context to the request body and fee + total_price to the response body of the POST /quote and GET /price requests; (ii) add fee to the response body of GET /quote/:id; and (iii) allow sell_amount and buy_amount in the responses to be different from the ones sent in the request. (#1204)
v1.6.1: Add note about expires_at and expires_after and their relationship. (#1147)
v1.6.0: Make SEP-10 authentication token optional for the GET /info, GET /price and GET /prices endpoints. (#1144)

Files

sep-0038.md

Latest commit

History

sep-0038.md

File metadata and controls

Preamble

Summary

Motivation

Specification

stellar.toml

Authentication

Content Type

Errors

Status Code

Asset Identification Format

Endpoints

GET Info

Authentication

Request

Response

Example

GET Prices

Authentication

Request

Response

Examples

GET Price

Authentication

Request

Response

Examples

Price Formulas

POST Quote

Protecting Against Bad Actors

Transaction Fees

Authentication

Request

Response

GET Quote

Authentication

Request

Response

Example

Changelog