Initial Commit

README.md

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+# KiwiOS Go Utilities
+
+This repository offers various utility packages for Go artifacts in KiwiOS. It does not provide any direct executable.
+
+## GatewayJWT
+
+Provides the function `GetGatewayJWT(tokenURL string)` which fetches a JWT from the [Gateway Identity Service](https://bitbucket.dev.kiwigrid.com/projects/GM/repos/gateway-registry). This JWT can be used to authenticate against Kiwigrid Cloud services.
+
+The `tokenURL` is usually retrieved via the [gateway-registry-bridge](https://bitbucket.dev.kiwigrid.com/projects/BOSS/repos/gateway-registry-bridge).

gatewayjwt/jwt.go

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+package gatewayjwt
+
+import (
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/dgrijalva/jwt-go"
+)
+
+var client = &http.Client{}
+var gatewayID = ""
+var gatewayKey = ""
+
+func fetchAuthTokens() error {
+	cmdline, err := ioutil.ReadFile("/proc/cmdline")
+	if err != nil {
+		return err
+	}
+
+	args := strings.Fields(string(cmdline))
+	for _, v := range args {
+		if strings.HasPrefix(v, "kg.gateway.id=") {
+			gatewayID = v[14:]
+		} else if strings.HasPrefix(v, "kg.gateway.key=") {
+			gatewayKey = v[15:]
+		}
+	}
+
+	if gatewayID == "" || gatewayKey == "" {
+		return errors.New("Cannot read gateway id or key")
+	}
+
+	return nil
+}
+
+// GetGatewayJWT fetches a JWT from the IoT Identity Service used for authenticating against various Kiwigrid services.
+func GetGatewayJWT(tokenURL string) (string, error) {
+	if gatewayID == "" || gatewayKey == "" {
+		err := fetchAuthTokens()
+		if err != nil {
+			return "", err
+		}
+	}
+
+	claims := &jwt.StandardClaims{
+		ExpiresAt: time.Now().Add(30 * time.Minute).Unix(),
+		Issuer:    gatewayID,
+		Subject:   gatewayID,
+	}
+
+	clientJwt, err := jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString([]byte(gatewayKey))
+
+	if err != nil {
+		return "", err
+	}
+
+	req, err := http.NewRequest("POST", tokenURL, nil)
+	req.Header.Add("Authorization", "Bearer "+clientJwt)
+	req.Header.Add("Accept", "application/json")
+	req.Header.Add("Content-Type", "application/json")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+
+	var data map[string]interface{}
+
+	if err := json.Unmarshal(body, &data); err != nil {
+		return "", err
+	}
+
+	return data["access_token"].(string), nil
+}

go.mod

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+module bitbucket.dev.kiwigrid.com/BOSS/kiwios-go-utils
+
+go 1.13
+
+require github.com/dgrijalva/jwt-go v3.2.0+incompatible

go.sum

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+github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
+github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=