# Sign In Customer

Sign-in from a backend service on behalf of a consumer customer (B2C) or customer delegate (B2B).
Used by custom integrations and e-commerce plugins as a form of single-sign-on for the checkout.
If the customer has been authenticated with the merchant's website, this lets them also authenticate
a known customer with April. This is a pre-requisite for using the checkout for a B2B customer.

For both B2B and B2C customers having an authenticated session with the checkout also unlocks access
to saved cards as a payment source.

Note merchants need to have been registered as supporting B2B customer when onboarded to be able to
support B2B customers in the checkout.

Endpoint: POST /auth/signin
Version: 3.0
Security: Marketplace API Key | Merchant Secret Token | Pay By Link Token

## Header parameters:

  - `Merchant-Id` (string)
    Perform operation in the context of the given merchant. Usually not required — specify only if acting on behalf of a merchant not implied by the credentials specified in the Authorization header.

## Response 200 fields (application/json):

  - `customerId` (string, required)
    System unique identifier for the customer

  - `customerDelegateId` (string)
    System unique identifier for the customer delegate

  - `customToken` (string, required)
    A custom token that can be provided to the checkout.

## Response 400 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 401 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 403 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 404 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 405 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 406 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 409 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 422 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 429 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 500 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata

## Response 503 fields (application/json):

  - `statusCode` (integer, required)
    HTTP status code for this error

  - `errorCode` (string, required)
    An April code providing a brief explanation of the underlying error. Use this if you wish to provide custom behaviour based on the error type.

  - `message` (string, required)
    Human readable description of the error

  - `tracer` (string)
    An unique identifier for the request. Provide this to the support team if you wish to query a particular error.

  - `detail` (string)
    Optional additional details for the error.

  - `errorTypeDescription` (string)
    A description of the category of errors for the given statusCode.

  - `metadata` (any)
    Optional key value list of metadata