token: extra numeric values + test TokenType case

+ Added tests for TokenType by checking case.
+ Added numeric conversion for float and integer like
  values from token.Extra.

Change-Id: I0909a4458ed58e33428afbf40478a668d150dda7
Reviewed-on: https://go-review.googlesource.com/15156
Reviewed-by: Andrew Gerrand <adg@golang.org>

token.go

@@ -7,6 +7,7 @@ package oauth2
 import (
 	"net/http"
 	"net/url"
+	"strconv"
 	"strings"
 	"time"
 
@@ -92,14 +93,28 @@ func (t *Token) WithExtra(extra interface{}) *Token {
 // Extra fields are key-value pairs returned by the server as a
 // part of the token retrieval response.
 func (t *Token) Extra(key string) interface{} {
-	if vals, ok := t.raw.(url.Values); ok {
-		// TODO(jbd): Cast numeric values to int64 or float64.
-		return vals.Get(key)
-	}
 	if raw, ok := t.raw.(map[string]interface{}); ok {
 		return raw[key]
 	}
-	return nil
+
+	vals, ok := t.raw.(url.Values)
+	if !ok {
+		return nil
+	}
+
+	v := vals.Get(key)
+	switch s := strings.TrimSpace(v); strings.Count(s, ".") {
+	case 0: // Contains no "."; try to parse as int
+		if i, err := strconv.ParseInt(s, 10, 64); err == nil {
+			return i
+		}
+	case 1: // Contains a single "."; try to parse as float
+		if f, err := strconv.ParseFloat(s, 64); err == nil {
+			return f
+		}
+	}
+
+	return v
 }
 
 // expired reports whether the token is expired.