box: fix reconnect failing with HTTP 400 Bad Request

The error is:

  Error: failed to configure token with jwt authentication: jwtutil: failed making auth request: 400 Bad Request

With the following additional debug information:

  jwtutil: Response Body: {"error":"invalid_grant","error_description":"Please check the 'aud' claim. Should be a string"}

Problem is that in jwt-go the RegisteredClaims type has Audience field (aud claim) that
is a list, while box apparantly expects it to be a singular string. In jwt-go v4 we
currently use there is an alternative type StandardClaims which matches what box wants.
Unfortunately StandardClaims is marked as deprecated, and is removed in the
newer v5 version, so we this is a short term fix only.

Fixes #7114

backend/box/box.go

@@ -77,7 +77,7 @@ var (
 )
 
 type boxCustomClaims struct {
-	jwt.RegisteredClaims
+	jwt.StandardClaims
 	BoxSubType string `json:"box_sub_type,omitempty"`
 }
 
@@ -206,12 +206,14 @@ func getClaims(boxConfig *api.ConfigJSON, boxSubType string) (claims *boxCustomC
 	}
 
 	claims = &boxCustomClaims{
-		RegisteredClaims: jwt.RegisteredClaims{
-			ID:        val,
+		//lint:ignore SA1019 since we need to use jwt.StandardClaims even if deprecated in jwt-go v4 until a more permanent solution is ready in time before jwt-go v5 where it is removed entirely
+		//nolint:staticcheck // Don't include staticcheck when running golangci-lint to avoid SA1019
+		StandardClaims: jwt.StandardClaims{
+			Id:        val,
 			Issuer:    boxConfig.BoxAppSettings.ClientID,
 			Subject:   boxConfig.EnterpriseID,
-			Audience:  jwt.ClaimStrings{tokenURL},
-			ExpiresAt: jwt.NewNumericDate(time.Now().Add(time.Second * 45)),
+			Audience:  tokenURL,
+			ExpiresAt: time.Now().Add(time.Second * 45).Unix(),
 		},
 		BoxSubType: boxSubType,
 	}