/// <summary>
/// Verifies the capability chain, if any, attached to the given capability.
/// </summary>
/// <param name="capability"></param>
/// <returns></returns>
public static async Task <JToken> VerifyCapabilityChain(JToken capability, PurposeOptions purposeOptions, JsonLdProcessorOptions options = null)
{
/* Verification process is:
* 1. Fetch capability if only its ID was passed.
* 1.1. Ensure `capabilityAction` is allowed.
* 2. Get the capability delegation chain for the capability.
* 3. Validate the capability delegation chain.
* 4. Verify the root capability:
* 4.1. Check the expected target, if one was specified.
* 4.2. Ensure that the caveats are met on the root capability.
* 4.3. Ensure root capability is expected and has no invocation target.
* 5. If `excludeGivenCapability` is not true, then we need to verify the
* capability delegation proof on `capability`, so add it to the chain to
* get processed below.
* 6. For each capability `cap` in the chain, verify the capability delegation
* proof on `cap`. This will validate everything else for `cap` including
* that caveats are met.
*
* Note: We start verifying a capability from its root of trust (the
* beginning or head of the capability chain) as this approach limits an
* attacker's ability to waste our time and effort traversing from the tail
* to the head.
*/
// 1. Fetch capability if only its ID was passed.
capability = await FetchInSecurityContextAsync(capability, false, options);
//capability = new CapabilityDelegation(cap as JObject);
// TODO: Add allowed action validation
// 2. Get the capability delegation chain for the capability.
var capabilityChain = GetCapabilityChain(capability);
// 3. Validate the capability delegation chain.
ValidateCapabilityChain(capability, capabilityChain);
// 4. Verify root capability (note: it must *always* be dereferenced since
// it does not need to have a delegation proof to vouch for its authenticity
// ... dereferencing it prevents adversaries from submitting an invalid
// root capability that is accepted):
var isRoot = !capabilityChain.Any();
var rootCapability = isRoot ? capability : capabilityChain.First();
capabilityChain = capabilityChain.Skip(1).ToArray();
rootCapability = await Utils.FetchInSecurityContextAsync(rootCapability, isRoot, null);
// 4.1. Check the expected target, if one was specified.
if (purposeOptions.ExpectedTarget != null)
{
var target = GetTarget(rootCapability);
if (target != purposeOptions.ExpectedTarget)
{
throw new Exception($"Expected target ({purposeOptions.ExpectedTarget}) does not match " +
$"root capability target({target}).");
}
}
// 4.2. Ensure that the caveats are met on the root capability.
// TODO: Add caveats
// 4.3. Ensure root capability is expected and has no invocation target.
// run root capability checks (note that these will only be run once
// because the `verifiedParentCapability` parameter stops recursion
// from happening below)
// ensure that the invocation target matches the root capability or,
// if `expectedRootCapability` is present, that it matches that
if (purposeOptions.ExpectedRootCapability != null)
{
if (purposeOptions.ExpectedRootCapability != rootCapability["id"].Value <string>())
{
throw new Exception($"Expected root capability ({purposeOptions.ExpectedRootCapability}) does not " +
$"match actual root capability({rootCapability["id"]}).");
}
}
else if (GetTarget(rootCapability) != rootCapability["id"].Value <string>())
{
throw new Exception("The root capability must not specify a different " +
"invocation target.");
}
// root capability now verified
var verifiedParentCapability = rootCapability;
// if verifying a delegation proof and we're at the root, exit early
if (isRoot)
{
return(verifiedParentCapability);
}
// create a document loader that will use properly embedded capabilities
var documentLoader = new CachingDocumentLoader(Array.Empty <IDocumentResolver>());
var next = capabilityChain;
while (next.Any())
{
// the only capability that may be embedded (if the zcap is valid) is
// the last one in the chain, if it is embedded, add it to `dlMap` and
// recurse into its chain and loop to collect all embedded zcaps
var cap = next.Last();
if (!(cap is JObject))
{
break;
}
if (cap["@context"] == null)
{
// the capabilities in the chain are already in the security context
// if no context has been specified
cap["@context"] = Constants.SECURITY_CONTEXT_V2_URL;
}
// Transforms the `capability` into the security context (the native
// context this code uses) so we can process it cleanly and then
// verifies the capability delegation proof on `capability`. This allows
// capabilities to be expressed using custom contexts.
cap = await FetchInSecurityContextAsync(cap, false, options);
documentLoader.AddCached(cap["id"].Value <string>(), cap as JObject);
next = GetCapabilityChain(cap);
}
options.DocumentLoader = documentLoader.Load;
// 5. If `excludeGivenCapability` is not true, then we need to verify the
// capability delegation proof on `capability`, so add it to the chain to
// get processed below. If an `inspectCapabilityChain` handler has been
// provided, the verify results are required on all capabilities.
// TODO: Add support for `excludeGivenCapability`
// 6. For each capability `cap` in the chain, verify the capability
// delegation proof on `cap`. This will validate everything else for
// `cap` including that caveats are met.
// note that `verifiedParentCapability` will prevent repetitive checking
// of the same segments of the chain (once a parent is verified, its chain
// is not checked again when checking its children)
for (int i = 0; i < capabilityChain.Count(); i++)
{
var cap = capabilityChain.ElementAt(i);
cap = await FetchInSecurityContextAsync(cap, false, options);
var verifyResult = LdSignatures.VerifyAsync(cap, new ProofOptions
{
Suite = purposeOptions.Suite,
Purpose = new CapabilityDelegationProofPurpose
{
Options = new PurposeOptions
{
ExpectedTarget = purposeOptions.ExpectedTarget,
ExpectedRootCapability = purposeOptions.ExpectedRootCapability
},
VerifiedParentCapability = verifiedParentCapability
},
DocumentLoader = documentLoader,
CompactProof = false
});
}
return(null);
}
public CapabilityInvocation(PurposeOptions options) : base("capabilityInvocation")
{
Options = options;
}
