Use env for config instead of flags

.env

@@ -0,0 +1,2 @@
+LISTEN=:8080
+SECRET=secret

Dockerfile

@@ -3,12 +3,13 @@ FROM golang:1.11-rc-alpine as build
 RUN apk add --no-cache git=2.18.1-r0
 
 WORKDIR /src
-COPY go.mod go.sum *.go ./
+COPY go.mod go.sum .env *.go ./
 RUN go get -d -v ./...
 RUN CGO_ENABLED=0 go build -ldflags "-s -w"
 
 FROM scratch
 
 COPY --from=build /src/login /login
+COPY --from=build /src/.env /.env
 
 ENTRYPOINT ["/login"]

README.md

@@ -2,6 +2,15 @@
 
 Beep backend handling login. For now, just a POST endpoint returning a JWT. In the furture, SMS-based perpetual login.
 
+## Environment variables
+
+Supply environment variables by either exporting them or editing ```.env```.
+
+| ENV | Description | Default |
+| ---- | ----------- | ------- |
+| LISTEN | Host and port number to listen on | :8080 |
+| SECRET | JWT secret | secret |
+
 ## API (temporary)
 
 ```

go.mod

@@ -2,5 +2,6 @@ module login
 
 require (
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible
+	github.com/joho/godotenv v1.3.0
 	github.com/julienschmidt/httprouter v1.2.0
 )

go.sum

@@ -1,4 +1,6 @@
 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=
+github.com/joho/godotenv v1.3.0 h1:Zjp+RcGpHhGlrMbJzXTrZZPrWj+1vfm90La1wgB6Bhc=
+github.com/joho/godotenv v1.3.0/go.mod h1:7hK45KPybAkOC6peb+G5yklZfMxEjkZhHbwpqxOKXbg=
 github.com/julienschmidt/httprouter v1.2.0 h1:TDTW5Yz1mjftljbcKqRcrYhd4XeOoI98t+9HbQbYf7g=
 github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7VTCxuUUipMqKk8s4w=

main.go

@@ -2,10 +2,11 @@ package main
 
 import (
   "encoding/json"
-  "flag"
   "log"
   "net/http"
+  "os"
 
+  "github.com/joho/godotenv"
   "github.com/julienschmidt/httprouter"
   "github.com/dgrijalva/jwt-go"
 )
@@ -14,11 +15,13 @@ var listen string
 var secret []byte
 
 func main() {
-  var s string
-  // Parse flags
-	flag.StringVar(&listen, "listen", ":8080", "host and port to listen on")
-  flag.StringVar(&s, "secret", "secret", "JWT secret")
-  flag.Parse()
+  // Load .env
+  err := godotenv.Load()
+  if err != nil {
+    log.Fatal("Error loading .env file")
+  }
+  listen = os.Getenv("LISTEN")
+  s := os.Getenv("SECRET")
 
   secret = []byte(s)