Adding a provider for CloudFoundry's UAA OAuth

* Added a cloudfoundry provider (cloudfoundry.go) to interface with cloudfoundry's UAA [1]
* Provide defaults for local Cloudfoundry installation on BOSH lite [2]
* One workaround for UAA bug [3] in provider_default is necessary, but only applied
  if provider "cloudfoundry" is used

[1] https://github.com/cloudfoundry/uaa
[2] https://github.com/cloudfoundry/bosh-lite
[3] cloudfoundry/uaa#308

providers/cloudfoundry.go

@@ -0,0 +1,77 @@
+package providers
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/url"
+)
+
+type CloudFoundryProvider struct {
+	*ProviderData
+}
+
+func NewCloudFoundryProvider(p *ProviderData) *CloudFoundryProvider {
+	p.ProviderName = "CloudFoundry"
+	// Defaults for Bosh-Lite, must be configured for other OAuth Endpoints.
+	if p.LoginURL == nil || p.LoginURL.String() == "" {
+		p.LoginURL = &url.URL{
+                        Scheme: "http",
+                        Host:   "login.bosh-lite.com",
+                        Path:   "/oauth/authorize",
+                }
+	}
+	if p.RedeemURL == nil || p.RedeemURL.String() == "" {
+		p.RedeemURL = &url.URL{
+                        Scheme: "http",
+                        Host:   "login.bosh-lite.com",
+                        Path:   "/oauth/token",
+                }
+	}
+	if p.ValidateURL == nil || p.ValidateURL.String() == "" {
+		p.ValidateURL = &url.URL{
+                        Scheme: "http",
+                        Host:   "login.bosh-lite.com",
+                        Path:   "/userinfo",
+                }
+	}
+	if p.Scope == "" {
+		p.Scope = "openid"
+	}
+	return &CloudFoundryProvider{ProviderData: p}
+}
+
+func (p *CloudFoundryProvider) GetEmailAddress(s *SessionState) (string, error) {
+
+	var email struct {
+		Email   string `json:"email"`
+	}
+
+	params := url.Values{
+		"access_token": {s.AccessToken},
+	}
+	endpoint := p.ValidateURL.String() + "?" + params.Encode()
+	resp, err := http.DefaultClient.Get(endpoint)
+	if err != nil {
+		return "", err
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if err != nil {
+		return "", err
+	}
+
+	if resp.StatusCode != 200 {
+		return "", fmt.Errorf("got %d from %q %s", resp.StatusCode, endpoint, body)
+	} else {
+		log.Printf("got %d from %q %s", resp.StatusCode, endpoint, body)
+	}
+
+	if err := json.Unmarshal(body, &email); err != nil {
+		return "", fmt.Errorf("%s unmarshaling %s", err, body)
+	}
+
+	return email.Email, nil
+}

providers/provider_default.go

@@ -35,6 +35,10 @@ func (p *ProviderData) Redeem(redirectURL, code string) (s *SessionState, err er
 		return
 	}
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	// workaround for Cloudfoundry UAA bug https://github.com/cloudfoundry/uaa/issues/308
+	if (p.ProviderName == "CloudFoundry") {
+		req.SetBasicAuth(p.ClientID, p.ClientSecret)
+	}
 
 	var resp *http.Response
 	resp, err = http.DefaultClient.Do(req)

providers/providers.go

@@ -26,6 +26,8 @@ func New(provider string, p *ProviderData) Provider {
 		return NewGitHubProvider(p)
 	case "azure":
 		return NewAzureProvider(p)
+	case "cloudfoundry":
+		return NewCloudFoundryProvider(p)
 	default:
 		return NewGoogleProvider(p)
 	}