compute.go

Documentation: google.golang.org/api/idtoken

     1  // Copyright 2020 Google LLC.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package idtoken
     6  
     7  import (
     8  	"fmt"
     9  	"net/url"
    10  	"time"
    11  
    12  	"cloud.google.com/go/compute/metadata"
    13  	"golang.org/x/oauth2"
    14  
    15  	"google.golang.org/api/internal"
    16  )
    17  
    18  // computeTokenSource checks if this code is being run on GCE. If it is, it will
    19  // use the metadata service to build a TokenSource that fetches ID tokens.
    20  func computeTokenSource(audience string, ds *internal.DialSettings) (oauth2.TokenSource, error) {
    21  	if ds.CustomClaims != nil {
    22  		return nil, fmt.Errorf("idtoken: WithCustomClaims can't be used with the metadata service, please provide a service account if you would like to use this feature")
    23  	}
    24  	ts := computeIDTokenSource{
    25  		audience: audience,
    26  	}
    27  	tok, err := ts.Token()
    28  	if err != nil {
    29  		return nil, err
    30  	}
    31  	return oauth2.ReuseTokenSource(tok, ts), nil
    32  }
    33  
    34  type computeIDTokenSource struct {
    35  	audience string
    36  }
    37  
    38  func (c computeIDTokenSource) Token() (*oauth2.Token, error) {
    39  	v := url.Values{}
    40  	v.Set("audience", c.audience)
    41  	v.Set("format", "full")
    42  	urlSuffix := "instance/service-accounts/default/identity?" + v.Encode()
    43  	res, err := metadata.Get(urlSuffix)
    44  	if err != nil {
    45  		return nil, err
    46  	}
    47  	if res == "" {
    48  		return nil, fmt.Errorf("idtoken: invalid response from metadata service")
    49  	}
    50  	return &oauth2.Token{
    51  		AccessToken: res,
    52  		TokenType:   "bearer",
    53  		// Compute tokens are valid for one hour, leave a little buffer
    54  		Expiry: time.Now().Add(55 * time.Minute),
    55  	}, nil
    56  }
    57
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