/*

    File:       ServerTrustChallengeHandler.m

    Contains:   Handles HTTPS server trust challenges.

    Written by: DTS

    Copyright:  Copyright (c) 2011 Apple Inc. All Rights Reserved.

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*/

#import "ServerTrustChallengeHandler.h"

#import "Credentials.h"

#import "DebugOptions.h"

@interface ServerTrustChallengeHandler ()

@property (nonatomic, retain, readwrite) UIAlertView *  alertView;

@end

@implementation ServerTrustChallengeHandler

+ (void)registerHandlers

    // Called by the handler registry within ChallengeHandler to request that the 

    // concrete subclass register itself.

{

    // We observe the serverValidation debug option and, when it changes, either register 

    // or deregister ourselves based on the value of the option.  We pass in 

    // NSKeyValueObservingOptionInitial so that our observer is called immediately, and this 

    // then sets up our initial state.

    [[DebugOptions sharedDebugOptions] addObserver:self forKeyPath:@"serverValidation" options:NSKeyValueObservingOptionInitial context:NULL];

}

+ (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

    // A KVO callback called when the serverValidation debug option changes.  If the user 

    // has requested default validation, we pull ourselves out of the registry, otherwise we 

    // make sure we're in there.

{

    if ( (object == [DebugOptions sharedDebugOptions]) && [keyPath isEqual:@"serverValidation"] ) {

        // The following code relies on two properties of challenge handling registration:

        //

        // o It's OK to deregister a handler that's not registered.

        // o It's OK to register a handler that's already registered.

        //

        // Without these two properties this code would have to keep track of whether it's 

        // registered or not, which would be less fun.

        if ([DebugOptions sharedDebugOptions].serverValidation == kDebugOptionsServerValidationDefault) {

            [ChallengeHandler deregisterHandlerClass:[self class] forAuthenticationMethod:NSURLAuthenticationMethodServerTrust];

        } else {

            [ChallengeHandler registerHandlerClass:[self class] forAuthenticationMethod:NSURLAuthenticationMethodServerTrust];

        }

    } else {

        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];

    }

}

- (void)dealloc

{

    assert(self.alertView == nil);

    [super dealloc];

}

#pragma mark * Core code

@synthesize alertView = _alertView;

static SecCertificateRef SecTrustGetLeafCertificate(SecTrustRef trust)

    // Returns the leaf certificate from a SecTrust object (that is always the 

    // certificate at index 0).

{

    SecCertificateRef   result;

    assert(trust != NULL);

    if (SecTrustGetCertificateCount(trust) > 0) {

        result = SecTrustGetCertificateAtIndex(trust, 0);

        assert(result != NULL);

    } else {

        result = NULL;

    }

    return result;

}

static NSMutableDictionary * sSiteToCertificateMap;     // keys are host names as NSString 

                                                        // values are SecCertificateRef

+ (void)resetTrustedCertificates

{

    // We don't just release the entire array because the _serverTrustResolvedWithSuccess 

    // code assumes that, if execution gets that far, sSiteToCertificateMap is not nil.

    if (sSiteToCertificateMap != nil) {

        [sSiteToCertificateMap removeAllObjects];

    }

}

- (void)_serverTrustResolvedWithSuccess:(BOOL)success rememberSuccess:(BOOL)rememberSuccess

    // Some common code that's called in a variety of places to finally resolve the 

    // challenge.  Also, if rememberSuccess is set, we add an entry for this challenge 

    // into sSiteToCertificateMap so that future challenges can be automatically resolved.

{

    NSURLCredential *   credential;

    // ! success && rememberSuccess is a weird combination, but we allow is so 

    // that our clients don't have to jump through too many hoops.

    // On succes, create a credential with which to resolve the challenge.

    credential = nil;

    if (success) {

        NSURLProtectionSpace *  protectionSpace;

        SecTrustRef             trust;

        NSString *              host;

        SecCertificateRef       serverCert;

        protectionSpace = [self.challenge protectionSpace];

        assert(protectionSpace != nil);

        trust = [protectionSpace serverTrust];

        assert(trust != NULL);

        credential = [NSURLCredential credentialForTrust:trust];

        assert(credential != nil);

        // If we've been asked to remember the response, do so now.

        if (rememberSuccess) {

            assert(sSiteToCertificateMap != nil);

            host = [[self.challenge protectionSpace] host];

            assert(host != nil);

            if ( [sSiteToCertificateMap objectForKey:host] == nil ) {

                serverCert = SecTrustGetLeafCertificate(trust);

                if (serverCert != NULL) {

                    [sSiteToCertificateMap setObject:(id)serverCert forKey:host];

                }

            }

        }

    }

    // Pass the final credential to the base class's stop code (which in turn 

    // tells us to tear down our UI) and then tell our delegate.

    [self stopWithCredential:credential];

    [self.delegate challengeHandlerDidFinish:self];

}

- (void)_evaluateAskPerUntrustedSiteTrust

    // Implements the kDebugOptionsServerValidationAskPerUntrustedSite server trust 

    // validation option.

{

    OSStatus                err;

    NSURLProtectionSpace *  protectionSpace;

    SecTrustRef             trust;

    BOOL                    trusted;

    SecTrustResultType      trustResult;

    SecCertificateRef       previousCert;

    protectionSpace = [self.challenge protectionSpace];

    assert(protectionSpace != nil);

    trust = [protectionSpace serverTrust];

    assert(trust != NULL);

    // Evaluate the trust the standard way.

    err = SecTrustEvaluate(trust, &trustResult);

    trusted = (err == noErr) && ((trustResult == kSecTrustResultProceed) || (trustResult == kSecTrustResultUnspecified));

    // If the standard policy says that it's trusted, allow it right now. 

    // Otherwise do our custom magic.

    if (trusted) {

        [self _serverTrustResolvedWithSuccess:YES rememberSuccess:NO];

    } else {

        if (sSiteToCertificateMap == nil) {

            sSiteToCertificateMap = [[NSMutableDictionary alloc] init];

            assert(sSiteToCertificateMap != nil);

        }

        // Check to see if we've previously seen this server.

        previousCert = (SecCertificateRef) [sSiteToCertificateMap objectForKey:[protectionSpace host]];

        assert( (previousCert == NULL) || (CFGetTypeID(previousCert) == SecCertificateGetTypeID()) );

        if (previousCert == NULL) {

            // We've not seen this server before.  Ask the user.

            assert(self.alertView == nil);

            self.alertView = [[[UIAlertView alloc] initWithTitle:@"ACCEPT WEBSITE CERTIFICATE" 

                message:@"THE CERTIFICATE FOR THIS WEBSITE IS INVALID. TAP ACCEPT TO CONNECT TO THIS WEBSITE ANYWAY." 

                delegate:self 

                cancelButtonTitle:@"Accept" 

                otherButtonTitles:@"Cancel", 

                nil

            ] autorelease];

            assert(self.alertView != nil);

            [self.alertView show];

            // continues in -alertView:clickedButtonAtIndex:

        } else {

            BOOL                success;

            SecCertificateRef   serverCert;

            // We've seen this server before.  Check to see whether the 

            // certificate from the connection matches the certificate 

            // we saw last time.  If so, allow the connection.  If not, 

            // deny the connection.

            success = NO;

            serverCert = SecTrustGetLeafCertificate(trust);

            if (serverCert != NULL) {

                CFDataRef       previousCertData;

                CFDataRef       serverCertData;

                previousCertData = SecCertificateCopyData(previousCert);

                serverCertData   = SecCertificateCopyData(serverCert  );

                assert(previousCertData != NULL);

                assert(serverCertData   != NULL);

                success = CFEqual(previousCertData, serverCertData);

                CFRelease(previousCertData);

                CFRelease(serverCertData);

            }

            if (success) {

                [self _serverTrustResolvedWithSuccess:YES rememberSuccess:NO];

            } else {

                [self _serverTrustResolvedWithSuccess:NO  rememberSuccess:NO];

            }

        }

    }

}

- (void)_evaluateImportedCertificatesTrust

    // Implements the kDebugOptionsServerValidationTrustImportedCertificates server 

    // trust validation option.

{

    OSStatus                err;

    NSURLProtectionSpace *  protectionSpace;

    SecTrustRef             trust;

    SecTrustResultType      trustResult;

    BOOL                    trusted;

    protectionSpace = [self.challenge protectionSpace];

    assert(protectionSpace != nil);

    trust = [protectionSpace serverTrust];

    assert(trust != NULL);

    // Evaluate the trust the standard way.

    err = SecTrustEvaluate(trust, &trustResult);

    trusted = (err == noErr) && ((trustResult == kSecTrustResultProceed) || (trustResult == kSecTrustResultUnspecified));

    // If that fails, apply our certificates as anchors and see if that helps.

    // 

    // It's perfectly acceptable to apply all of our certificates to the SecTrust 

    // object, and let the SecTrust object sort out the mess.  Of course, this assumes 

    // that the user trusts all certificates equally in all situations, which is implicit 

    // in our user interface; you could provide a more sophisticated user interface 

    // to allow the user to trust certain certificates for certain sites and so on).

    if ( ! trusted ) {

        err = SecTrustSetAnchorCertificates(trust, (CFArrayRef) [Credentials sharedCredentials].certificates);

        if (err == noErr) {

            err = SecTrustEvaluate(trust, &trustResult);

        }

        trusted = (err == noErr) && ((trustResult == kSecTrustResultProceed) || (trustResult == kSecTrustResultUnspecified));

    }

    if (trusted) {

        [self _serverTrustResolvedWithSuccess:YES rememberSuccess:NO];

    } else {

        [self _serverTrustResolvedWithSuccess:NO  rememberSuccess:NO];

    }

}

- (void)_handleServerTrustChallenge

    // Handles a server trust challenge according to the serverValidation debug option. 

    // This is called out of -didStart, and thus can present UI.  However, it may 

    // or not present UI depending on the specific server trust and debug options.

{

    switch ( [DebugOptions sharedDebugOptions].serverValidation ) {

        default:

            // fall through

        case kDebugOptionsServerValidationDefault: {

            // We should never have got here because we deregister ourselves when 

            // the user selects the default case.

            assert(NO);

            [self _serverTrustResolvedWithSuccess:NO rememberSuccess:NO];

        } break;

        case kDebugOptionsServerValidationAskPerUntrustedSite: {

            [self _evaluateAskPerUntrustedSiteTrust];

        } break;

        case kDebugOptionsServerValidationTrustImportedCertificates: {

            [self _evaluateImportedCertificatesTrust];

        } break;

        case kDebugOptionsServerValidationDisabled: {

            // Just say yes.

            [self _serverTrustResolvedWithSuccess:YES rememberSuccess:NO];

        } break;

    }

}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex

    // An alert view delegate callback that's called when the alert is dismissed.  

    // We use the tapped button index to decide how to resolve the challenge.

{

    #pragma unused(alertView)

    assert(alertView == self.alertView);

    [self _serverTrustResolvedWithSuccess:(buttonIndex == 0) rememberSuccess:YES];

}

#pragma mark * Override points

- (void)didStart

    // Called by our base class to tell us to create our UI.

{

    [super didStart];

    [self _handleServerTrustChallenge];

}

- (void)willFinish

    // Called by our base class to tell us to tear down our UI.

{

    [super willFinish];

    // If an alert is still up, tear it down immediately.

    if (self.alertView != nil) {

        self.alertView.delegate = nil;

        [self.alertView dismissWithClickedButtonIndex:self.alertView.cancelButtonIndex animated:NO];

        self.alertView = nil;

    }

}

@end