fix MatchError on auth header parameter

Header parameter doesn't have a value without '=' then application will be error

Author: tsuyoshizawa

scala-oauth2-core/src/main/scala/scalaoauth2/provider/AccessTokenFetcher.scala

@@ -49,6 +49,7 @@ object AuthHeader extends AccessTokenFetcher {
       val pairs = REGEXP_DIV_COMMA.split(trimmedHeader).map { exp =>
         val (key, value) = exp.split("=", 2) match {
           case Array(k, v) => (k, v.replaceFirst("^\"", ""))
+          case Array(k) => (k, "")
         }
 
         (key, URLDecoder.decode(value.replaceFirst("\"$", ""), "UTF-8"))

scala-oauth2-core/src/test/scala/scalaoauth2/provider/AuthHeaderSpec.scala

@@ -71,4 +71,10 @@ class AuthHeaderSpec extends FlatSpec {
     result.token should be ("token1")
   }
 
+  it should "fetch illegal parameter without =" in {
+    val result = AuthHeader.fetch(createRequest(Some("""OAuth access_token_value,fizz=buzz,foo""")))
+    result.token should be ("access_token_value")
+    result.params("fizz") should be ("buzz")
+    result.params("foo") should be ("")
+  }
 }