feat: add exp field to JWT if expires_in is set

.changelog/6429.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+google_service_account_jwt: added `expires_in` attribute for generating `exp` claim.
+```

google-beta/data_source_google_service_account_jwt.go

@@ -1,8 +1,10 @@
 package google
 
 import (
+	"encoding/json"
 	"fmt"
 	"strings"
+	"time"
 
 	iamcredentials "google.golang.org/api/iamcredentials/v1"
 
@@ -18,6 +20,11 @@ func dataSourceGoogleServiceAccountJwt() *schema.Resource {
 				Required:    true,
 				Description: `A JSON-encoded JWT claims set that will be included in the signed JWT.`,
 			},
+			"expires_in": {
+				Type:        schema.TypeInt,
+				Optional:    true,
+				Description: "Number of seconds until the JWT expires. If set and non-zero an `exp` claim will be added to the payload derived from the current timestamp plus expires_in seconds.",
+			},
 			"target_service_account": {
 				Type:         schema.TypeString,
 				Required:     true,
@@ -40,6 +47,10 @@ func dataSourceGoogleServiceAccountJwt() *schema.Resource {
 	}
 }
 
+var (
+	dataSourceGoogleServiceAccountJwtNow = time.Now
+)
+
 func dataSourceGoogleServiceAccountJwtRead(d *schema.ResourceData, meta interface{}) error {
 	config := meta.(*Config)
 
@@ -49,10 +60,30 @@ func dataSourceGoogleServiceAccountJwtRead(d *schema.ResourceData, meta interfac
 		return err
 	}
 
+	payload := d.Get("payload").(string)
+
+	if expiresIn := d.Get("expires_in").(int); expiresIn != 0 {
+		var decoded map[string]interface{}
+
+		if err := json.Unmarshal([]byte(payload), &decoded); err != nil {
+			return fmt.Errorf("error decoding `payload` while adding `exp` field: %w", err)
+		}
+
+		decoded["exp"] = dataSourceGoogleServiceAccountJwtNow().Add(time.Duration(expiresIn) * time.Second).Unix()
+
+		payloadBytesWithExp, err := json.Marshal(decoded)
+
+		if err != nil {
+			return fmt.Errorf("error re-encoding `payload` while adding `exp` field: %w", err)
+		}
+
+		payload = string(payloadBytesWithExp)
+	}
+
 	name := fmt.Sprintf("projects/-/serviceAccounts/%s", d.Get("target_service_account").(string))
 
 	jwtRequest := &iamcredentials.SignJwtRequest{
-		Payload:   d.Get("payload").(string),
+		Payload:   payload,
 		Delegates: convertStringSet(d.Get("delegates").(*schema.Set)),
 	}
 

google-beta/data_source_google_service_account_jwt_test.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"strings"
 	"testing"
+	"time"
 
 	"fmt"
 
@@ -18,6 +19,7 @@ const (
 	jwtTestSubject          = "custom-subject"
 	jwtTestFoo              = "bar"
 	jwtTestComplexFooNested = "baz"
+	jwtTestExpiresIn        = 60
 )
 
 type jwtTestPayload struct {
@@ -28,6 +30,8 @@ type jwtTestPayload struct {
 	ComplexFoo struct {
 		Nested string `json:"nested"`
 	} `json:"complexFoo"`
+
+	Expiration int64 `json:"exp"`
 }
 
 func testAccCheckServiceAccountJwtValue(name, audience string) resource.TestCheckFunc {
@@ -78,6 +82,12 @@ func testAccCheckServiceAccountJwtValue(name, audience string) resource.TestChec
 			return fmt.Errorf("invalid 'foo', expected '%s', got '%s'", jwtTestComplexFooNested, payload.ComplexFoo.Nested)
 		}
 
+		expectedExpiration := dataSourceGoogleServiceAccountJwtNow().Add(jwtTestExpiresIn * time.Second).Unix()
+
+		if payload.Expiration != expectedExpiration {
+			return fmt.Errorf("invalid 'exp', expected '%d', got '%d'", expectedExpiration, payload.Expiration)
+		}
+
 		return nil
 	}
 }
@@ -89,6 +99,13 @@ func TestAccDataSourceGoogleServiceAccountJwt(t *testing.T) {
 	serviceAccount := getTestServiceAccountFromEnv(t)
 	targetServiceAccountEmail := BootstrapServiceAccount(t, getTestProjectFromEnv(), serviceAccount)
 
+	staticTime := time.Now()
+
+	// Override the current time with one that is set to a static value, to compare against later.
+	dataSourceGoogleServiceAccountJwtNow = func() time.Time {
+		return staticTime
+	}
+
 	resource.Test(t, resource.TestCase{
 		PreCheck:  func() { testAccPreCheck(t) },
 		Providers: testAccProviders,
@@ -99,6 +116,16 @@ func TestAccDataSourceGoogleServiceAccountJwt(t *testing.T) {
 					testAccCheckServiceAccountJwtValue(resourceName, targetAudience),
 				),
 			},
+			{
+				PreConfig: func() {
+					// Bump the hardcoded time to ensure terraform responds well to the JWT expiration changing.
+					staticTime = time.Now().Add(10 * time.Second)
+				},
+				Config: testAccCheckGoogleServiceAccountJwt(targetServiceAccountEmail),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckServiceAccountJwtValue(resourceName, targetAudience),
+				),
+			},
 		},
 	})
 }
@@ -115,6 +142,8 @@ data "google_service_account_jwt" "default" {
         nested: "%s"
       }
     })
+
+    expires_in = %d
 }
-`, targetServiceAccount, jwtTestSubject, jwtTestFoo, jwtTestComplexFooNested)
+`, targetServiceAccount, jwtTestSubject, jwtTestFoo, jwtTestComplexFooNested, jwtTestExpiresIn)
 }

website/docs/d/service_account_jwt.html.markdown

@@ -23,6 +23,8 @@ data "google_service_account_jwt" "foo" {
     foo: "bar",
     sub: "subject",
   })
+
+  expires_in = 60
 }
 
 output "jwt" {
@@ -36,6 +38,7 @@ The following arguments are supported:
 
 * `target_service_account` (Required) - The email of the service account that will sign the JWT.
 * `payload` (Required) - The JSON-encoded JWT claims set to include in the self-signed JWT.
+* `expires_in` (Optional) - Number of seconds until the JWT expires. If set and non-zero an `exp` claim will be added to the payload derived from the current timestamp plus expires_in seconds.
 * `delegates` (Optional) - Delegate chain of approvals needed to perform full impersonation. Specify the fully qualified service account name.
 
 ## Attributes Reference