Add OAuth2 headers category to GRPCCall

src/objective-c/GRPCClient/GRPCCall+OAuth2.h

+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import "GRPCCall.h"
+
+// Helpers for setting and reading headers compatible with OAuth2.
+@interface GRPCCall (OAuth2)
+
+// Setting this property is equivalent to setting "Bearer <passed token>" as the value of the
+// request header with key "authorization" (the authorization header). Setting it to nil removes the
+// authorization header from the request.
+// The value obtained by getting the property is the OAuth2 bearer token if the authorization header
+// of the request has the form "Bearer <token>", or nil otherwise.
+@property(atomic, copy) NSString *oauth2_accessToken;
+
+// Returns the value (if any) of the "www-authenticate" response header (the challenge header).
+@property(atomic, readonly) NSString *oauth2_challengeHeader;
+
+@end

src/objective-c/GRPCClient/GRPCCall+OAuth2.m

+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import "GRPCCall+OAuth2.h"
+
+static NSString * const kAuthorizationHeader = @"authorization";
+static NSString * const kBearerPrefix = @"Bearer ";
+static NSString * const kChallengeHeader = @"www-authenticate";
+
+@implementation GRPCCall (OAuth2)
+
+- (NSString *)oauth2_accessToken {
+  NSString *headerValue = self.requestMetadata[kAuthorizationHeader];
+  if ([headerValue hasPrefix:kBearerPrefix]) {
+    return [headerValue substringFromIndex:kBearerPrefix.length];
+  } else {
+    return nil;
+  }
+}
+
+- (void)setOauth2_accessToken:(NSString *)token {
+  if (token) {
+    self.requestMetadata[kAuthorizationHeader] = [kBearerPrefix stringByAppendingString:token];
+  } else {
+    [self.requestMetadata removeObjectForKey:kAuthorizationHeader];
+  }
+}
+
+- (NSString *)oauth2_challengeHeader {
+  return self.responseMetadata[kChallengeHeader];
+}
+
+@end