Add cli helpers, move service-to-service into this package.

This probably could have been two changes, but here I really wasn't sure
what I wanted to get to until I was finished.

client/cliconfig/cliconfig.go

@@ -0,0 +1,100 @@
+// Package cliconfig provides integration with the codegangsta/cli library, so
+// that CLI applications that require auth can easily get their command-line
+// flags documented but integrated with what gog5auth requires.
+//
+// It is a separate package so that non-CLI packages won't end up pulling in
+// the CLI code when they are importing the rest of gog5auth.
+package cliconfig
+
+import (
+	"fmt"
+
+	"github.com/G5/gog5auth/client"
+	"github.com/codegangsta/cli"
+)
+
+// CLI flags that may be registered and validated against by this package. You
+// can use them in your own packages when you need to pull their values from
+// the cli.Context.
+const (
+	ClientIDFlag     = "g5-auth-client-id"
+	ClientSecretFlag = "g5-auth-client-secret"
+	EndpointFlag     = "g5-auth-endpoint"
+	UsernameFlag     = "g5-auth-username"
+	PasswordFlag     = "g5-auth-password"
+)
+
+var serviceToServiceIsRegistered bool
+
+// RegisterStandardFlags accepts an App to register flags that gog5auth
+// accepts. This registers the typical flags for application and auth server.
+// Should be paired with InitializeFromContext.
+func RegisterStandardFlags(app *cli.App) {
+	fs := []cli.Flag{
+		cli.StringFlag{
+			Name:   ClientIDFlag,
+			Usage:  "G5 Auth application ID",
+			EnvVar: "G5_AUTH_CLIENT_ID",
+		},
+		cli.StringFlag{
+			Name:   ClientSecretFlag,
+			Usage:  "G5 Auth application secret",
+			EnvVar: "G5_AUTH_CLIENT_SECRET",
+		},
+		cli.StringFlag{
+			Name:   EndpointFlag,
+			Value:  client.Endpoint,
+			Usage:  "G5 Auth endpoint",
+			EnvVar: "G5_AUTH_ENDPOINT",
+		},
+	}
+	app.Flags = append(app.Flags, fs...)
+}
+
+// InitializeFromContext sets all package-level variables based on the values
+// of cli flags, whether they come from environment variables or from
+// command-line flags. It will return an error if any required flag is not
+// present. Any by required, I mean any, because they're all required.
+//
+// It will check for the presence of more flags if
+// RegisterServiceToServiceFlags has been called.
+func InitializeFromContext(c *cli.Context) error {
+	reqd := map[*string]string{
+		&client.ClientID:     ClientIDFlag,
+		&client.ClientSecret: ClientSecretFlag,
+		&client.Endpoint:     EndpointFlag,
+	}
+	if serviceToServiceIsRegistered {
+		reqd[&client.ServiceAccountUsername] = UsernameFlag
+		reqd[&client.ServiceAccountPassword] = PasswordFlag
+	}
+	for toSet, flagName := range reqd {
+		s := c.String(flagName)
+		if s == "" {
+			return fmt.Errorf("missing required flag %s", flagName)
+		}
+		*toSet = s
+	}
+
+	return nil
+}
+
+// RegisterServiceToServiceFlags accepts an App to register flags that gog5auth
+// accepts. This registers the flags needed for service-to-service auth. Should
+// be paired with InitializeFromContext.
+func RegisterServiceToServiceFlags(app *cli.App) {
+	serviceToServiceIsRegistered = true
+	fs := []cli.Flag{
+		cli.StringFlag{
+			Name:   UsernameFlag,
+			Usage:  "G5 Auth Service Account Username",
+			EnvVar: "G5_AUTH_USERNAME",
+		},
+		cli.StringFlag{
+			Name:   PasswordFlag,
+			Usage:  "G5 Auth Service Account Password",
+			EnvVar: "G5_AUTH_PASSWORD",
+		},
+	}
+	app.Flags = append(app.Flags, fs...)
+}

client/config.go

@@ -3,6 +3,7 @@ package client
 import (
 	"errors"
 	"fmt"
+	"net/http"
 	"os"
 
 	"github.com/G5/oauth2"
@@ -12,9 +13,11 @@ import (
 // all are required. Use InitializeFromEnvironment to automatically set these
 // from G5-standard environment variable names.
 var (
-	Endpoint     = "auth.g5search.com"
-	ClientID     string
-	ClientSecret string
+	Endpoint               = "auth.g5search.com"
+	ClientID               string
+	ClientSecret           string
+	ServiceAccountUsername string
+	ServiceAccountPassword string
 )
 
 // InitializeFromEnvironment sets package-level configuration via G5-standard
@@ -67,3 +70,29 @@ func NewDefaultEndpoint() oauth2.Endpoint {
 		TokenURL: fmt.Sprintf("https://%s/oauth/token", Endpoint),
 	}
 }
+
+// ServiceToServiceClient instantiates a http.Client which will pass a token
+// with all of its requests. If a token cannot be aquired, the Client will be
+// nil and the error will show the issue. There will also be an error if the
+// ServiceAccountUsername and ServiceAccountPassword are not set.
+//
+// This will make a network request to the auth server immediately, and will
+// fail if there is a problem with any portion of the auth configuration.
+//
+// I am currently unsure of how the expiration of this token will affect the
+// client. There is information in the oauth2 documentation that suggests it
+// might refresh itself, but I have no tested it.
+func ServiceToServiceClient() (*oauth2.Config, *http.Client, error) {
+	if ServiceAccountUsername == "" || ServiceAccountPassword == "" {
+		return nil, nil, errors.New("missing ServiceAccountUsername/ServiceAccountPassword values")
+	}
+
+	conf := NewStandaloneConfig()
+	cl, err := PasswordAuthenticatedClientFromConfig(
+		conf,
+		ServiceAccountUsername, ServiceAccountPassword,
+		nil,
+	)
+
+	return conf, cl, err
+}