Method: token

Exchanges a credential for a Google OAuth 2.0 access token.

The token asserts an external identity within an identity pool, or it applies a Credential Access Boundary to a Google access token. Note that workforce pools do not support Credential Access Boundaries.

When you call this method, do not send the Authorization HTTP header in the request. This method does not require the Authorization header, and using the header can cause the request to fail.

HTTP request


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


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



The full resource name of the identity provider; for example: //<project-number>/locations/global/workloadIdentityPools/<pool-id>/providers/<provider-id> for workload identity pool providers, or //<pool-id>/providers/<provider-id> for workforce pool providers. Required when exchanging an external credential for a Google access token.



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.



Required. An identifier for the type of requested security token. Must be urn:ietf:params:oauth:token-type:access_token.



Required. The input token.

This token is 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 either urn:ietf:params:oauth:token-type:jwt or urn:ietf:params:oauth:token-type:idToken.

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 or ES256.

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

Example header:

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

Example payload:

  "iss": "",
  "iat": 1517963104,
  "exp": 1517966704,
  "sub": "113475438248934895348",
  "my_claims": {
    "additional_claim": "value"

If subjectToken is for AWS, it must be a serialized GetCallerIdentity token. This token contains the same information as a request to the AWS GetCallerIdentity() method, as well as the AWS signature for the request information. Use Signature Version 4. 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 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 value is typically set to the current time and is used to help prevent replay attacks.
    • host: The hostname of the url field; for example,
    • 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:

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

The following example shows a GetCallerIdentity token:

  "headers": [
    {"key": "x-amz-date", "value": "20200815T015049Z"},
    {"key": "Authorization",
    {"key": "x-goog-cloud-target-resource",
    {"key": "host", "value": ""}
.  ],
  "method": "POST",

If the token is a SAML 2.0 assertion, it must use the format defined in the SAML 2.0 spec, and the subjectTokenType must be urn:ietf:params:oauth:token-type:saml2. See Verification of external credentials for details on how SAML 2.0 assertions are validated during token exchanges.

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:access_token.

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



Required. An identifier that indicates the type of the security token in the subjectToken parameter. Supported values are urn:ietf:params:oauth:token-type:jwt, urn:ietf:params:oauth:token-type:id_token, urn:ietf:params:aws:token-type:aws4_request, urn:ietf:params:oauth:token-type:access_token, and urn:ietf:params:oauth:token-type:saml2.



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.

The size of the parameter value must not exceed 4096 characters.

Response body

Response message for v1.token.

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

JSON representation
  "access_token": string,
  "issued_token_type": string,
  "token_type": string,
  "expires_in": integer


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.



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



The type of access token. Always has the value Bearer.



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

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