Method: token

Exchanges a credential for a Google OAuth 2.0 access token.

The token asserts an external identity within a workload identity pool, or it applies a Credential Access Boundary to a Google access token.

HTTP request

POST https://sts.googleapis.com/v1beta/token

The URL uses gRPC Transcoding syntax.

Request body

The request body contains data with the following structure:

JSON representation 
{
  "grantType": string,
  "audience": string,
  "scope": string,
  "requestedTokenType": string,
  "subjectToken": string,
  "subjectTokenType": string,
  "options": string
}
Fields
grantType

string

Required. The grant type. Must be urn:ietf:params:oauth:grant-type:token-exchange, which indicates a token exchange.
audience

string

The full resource name of the identity provider. For example, //iam.googleapis.com/projects/<project-number>/workloadIdentityPools/<pool-id>/providers/<provider-id>. Required when exchanging an external credential for a Google access token.
scope

string

The OAuth 2.0 scopes to include on the resulting access token, formatted as a list of space-delimited, case-sensitive strings. Required when exchanging an external credential for a Google access token.
requestedTokenType

string

Required. The type of security token. Must be urn:ietf:params:oauth:token-type:accessToken, which indicates an OAuth 2.0 access token.
subjectToken

string

Required. The input token.

This token is a either an external credential issued by a workload identity pool provider, or a short-lived access token issued by Google.

If the token is an OIDC JWT, it must use the JWT format defined in RFC 7523, and the subjectTokenType must be urn:ietf:params:oauth:token-type:jwt.

The following headers are required:

  • kid: The identifier of the signing key securing the JWT.
  • alg: The cryptographic algorithm securing the JWT. Must be RS256.

The following payload fields are required. For more information, see RFC 7523, Section 3:

  • iss: The issuer of the token. The issuer must provide a discovery document at /.well-known/openid-configuration, formatted according to section 4.2 of the OIDC 1.0 Discovery specification.
  • iat: The issue time, in seconds, since the Unix epoch. Must be in the past.
  • exp: The expiration time, in seconds, since the Unix epoch. Must be less than 48 hours after iat. Shorter expiration times are more secure. If possible, we recommend setting an expiration time less than 6 hours.
  • sub: The identity asserted in the JWT.
  • aud: Configured by the mapper policy. The default value is the service account's unique ID.

Example header:

{
  "alg": "RS256",
  "kid": "us-east-11"
}

Example payload:

{
  "iss": "https://accounts.google.com",
  "iat": 1517963104,
  "exp": 1517966704,
  "aud": "113475438248934895348",
  "sub": "113475438248934895348",
  "my_claims": {
    "additional_claim": "value"
  }
}

If subjectToken is an AWS token, it must be a serialized, signed request to the AWS GetCallerIdentity() method. Format the request as URL-encoded JSON, and set the subjectTokenType parameter to urn:ietf:params:aws:token-type:aws4_request.

The following parameters are required:

  • url: The URL of the AWS STS endpoint for GetCallerIdentity(), such as https://sts.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15. Regional endpoints are also supported.
  • method: The HTTP request method: POST.
  • headers: The HTTP request headers, which must include:
  • Authorization: The request signature.
  • x-amz-date: The time you will send the request, formatted as an ISO8601 Basic string. This is typically set to the current time and used to prevent replay attacks.
  • host: The hostname of the url field; for example, sts.amazonaws.com.
  • x-goog-cloud-target-resource: The full, canonical resource name of the workload identity pool provider, with or without an https: prefix. To help ensure data integrity, we recommend including this header in the SignedHeaders field of the signed request. For example:
//iam.googleapis.com/projects/<project-number>/locations/<location>/workloadIdentityPools/<pool-id>/providers/<provider-id>
https://iam.googleapis.com/projects/<project-number>/locations/<location>/workloadIdentityPools/<pool-id>/providers/<provider-id>

If you are using temporary security credentials provided by AWS, you must also include the header x-amz-security-token, with the value <session-token>.

The following example shows a signed, serialized request:

{
  "headers":[
    {"key": "x-amz-date", "value": "20200815T015049Z"},
    {"key": "Authorization",
     "value":
     "AWS4-HMAC-SHA256+Credential=$credential,+SignedHeaders=host;x-amz-date;x-goog-cloud-target-resource,+Signature=$signature"},
    {"key": "x-goog-cloud-target-resource",
     "value":
     "//iam.googleapis.com/projects/<project-number>/locations/<location>/workloadIdentityPools/<pool-id>/providers/<provider-id>"},
    {"key": "host", "value": "sts.amazonaws.com"}
.  ],
  "method":"POST",
  "url":"https://sts.amazonaws.com?Action=GetCallerIdentity&Version=2011-06-15"
}

You can also use a Google-issued OAuth 2.0 access token with this field to obtain an access token with new security attributes applied, such as a Credential Access Boundary. In this case, set subjectTokenType to urn:ietf:params:oauth:token-type:accessToken.

If an access token already contains security attributes, you cannot apply additional security attributes.
subjectTokenType

string

Required. urn:ietf:params:oauth:token-type:accessToken.
options

string

A set of features that Security Token Service supports, in addition to the standard OAuth 2.0 token exchange, formatted as a serialized JSON object of Options.

Response body

If successful, the response body contains data with the following structure:

Response message for v1beta.token.

JSON representation 
{
  "access_token": string,
  "issued_token_type": string,
  "token_type": string,
  "expires_in": integer
}
Fields
access_token

string

An OAuth 2.0 security token, issued by Google, in response to the token exchange request.

Tokens can vary in size, depending in part on the size of mapped claims, up to a maximum of 12288 bytes (12 KB). Google reserves the right to change the token size and the maximum length at any time.
issued_token_type

string

The token type. Always matches the value of requestedTokenType from the request.
token_type

string

The type of accessToken. Always has the value Bearer.
expires_in

integer

The amount of time, in seconds, between the time when the accessToken was issued and the time when the accessToken will expire.

This field is absent when the subjectToken in the request is a Google-issued, short-lived access token. In this case, the accessToken has the same expiration time as the subjectToken.