Hence, welcome to one back-to-basics installment! Up to you!
Validate Access Tokens
Why Do We Validate Tokens? Why do we bother validating tokens, indeed?
Your responsibility shifts from verifying raw credentials to verifying that your caller did indeed token verification through your identity provider of choice and successfully authenticated.
The identity provider represents successful authentication operations by issuing a token, hence your job now becomes validating that token. More about what that entails in just a moment. Tokens are the form that issued credentials take to be transported, from authority to client and from client to resource.
Verifying a JSON Web Token
In other words, protocols are used for moving tokens. Mechanics of Token Validation Alrighty, what that that really mean to validate a token?
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- JSON Web Tokens - samuray-club.com
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When can you say that a token is well-formed? If the following holds: A.
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The token is correctly formatted according to its intended format B. The token has not been tampered with The meaning of A. Verifying those is just a matter of parsing the values and comparing those with the local time of the authority, modulo any clock skew if known.
All the token formats I listed establish that a token must be digitally signed by the authority that issues it. A digital signature is an operation which combines the data you want to protect and another will known piece of data, called a key.
If you receive an access token from an identity provider IdPin general, you don't need to validate it. You can pass it to the issuing IdP and the IdP takes care of the rest. See Identity Provider Access Tokens for details. If any of these checks fail, the token is considered invalid, and the request must be rejected with Forbidden result. Perform standard JWT validation.
That token verification generates a third piece of data, called the signature. The signature is typically sent with the token, accompanied by information about how the signing operation took place which key was used, what specific algorithm was used.
Step 3: Verify the Claims Prerequisites The tasks in this section might be already handled by your library, SDK, or software framework. For example, user pool token handling and management are provided on token verification client side through the Amazon Cognito SDKs. Such libraries can help if you need to manually process tokens for server-side API processing or if you are using other programming languages. If your JWT does not conform to this structure, consider it invalid and do not accept it. Amazon Cognito generates two pairs of RSA cryptographic keys for each user pool.
An application receiving the token can perform the same operation, provided that it has access to the proper key: it can then compare the result with the signature it received — and if it comes out different, that means that something changed the token after issuance, invalidating it. Given their importance I must make one special mention for one special class of keys, X certificates.
In order to verify a signature places by a token verification key, an app receiving the token needs to have access to the certificate containing the corresponding public key.
The next checks enter in the merit of the specific issuer and app being accessed. Coming from the Intended Authority You outsource authentication token verification a given authority because you trust it — but as you do so, it becomes critical to be able to verify that authentication did take place with your authority of choice and no else.
Tokens are designed to token verification their origin as clearly and unambiguously as possible. There are two main mechanisms used here, often used together. Signature verification.
The key used to sign the issued token is uniquely associated to the issuing authority, hence a token signed with a key you know is associated to a certain authority gives you mathematical certainty modulo stolen keys that the token originated from that authority.
Issuer value. Every authority is characterized by a unique identifier, typically assigned as part of the representation of that authority within the protocol though which the token verification has been requested and received. That is often a URI.
Verifying a JSON Web Token - Amazon Cognito
Different token formats will typically carry that information in a specific place, like a particular claim type, that the validation logic will parse and compare with the expected value In classic claims-based identity, every authority has both its own key and its own identifier.
In scenarios including identity as a service, however, that might not be the case.
For example: in Windows Azure Active Directory the token token verification infrastructure is shared across multiple tenants, each representing a distinct business entity. The signature of issued tokens will be performed with the Windows Azure AD key, option chart to all, hence the main differentiation between tenant will be reflected by the different issuer identifier found in the token.
Intended for the Current Application Tokens usually token verification a claim meant to indicate the target app they have been issued for. As for the issuer, the identifier used to indicate the app is typically token verification representation of the app within the protocol used for obtaining the token.
That part durov tokens the token is often referred to as the audience of the token.
Its purpose is the same as the corresponding field in a bank check: ensuring that only the intended beneficiary can take advantage of it. Imagine that Contoso is using two different applications, A and B, from token verification different SaaS providers.
Say that token verification employee obtains a token for A and sends it over. A could take that token token verification use it to access B, pretending to be the employee: the authority token verification what B expects, the token has not been tampered with, it is still within its validity period… however, as soon as B verifies the audience, it will discover that the token was originally meant for A and not B itself — making the token invalid for accessing B and averting the token forwarding attack.
This check has an interesting property: whereas issuer token verification and signing keys are often discoverable from the authority via some specific mechanism metatada documents, for examplethe audience value must always be specified on a per-app basis.
JWT Authentication Tutorial - samuray-club.com
In other words, typically the only source of truth for what audience value should be considered valid for a particular resource is the resource itself — the developer includes that value as part of the resource configuration. Other Checks The checks described are the indispensible verifications one must perform to assess the validity of an incoming token. That is just the beginning, of course: knowing that the caller is actually Bob token token verification Contoso does not mean that he has access to the resource he is requesting — rather, this gives you the information you need for performing your subsequent authorization checks if necessary for the business logic your app implements.
Specific resources and app types might consider some subsequent checks so important that they should really be part of the token validation proper — examples include the value in the scope claim for OAuth2 bearer flows.
Many middlewares offer extensibility points you can use for injecting token verification own validation logic in the pipeline; but it is also common to add the extra checks directly in the app, in constructs typical of the stack used e.
In the token verification all it matters is that the logic is executed before access is granted, which in practice usually means before the interesting app code gets to execute. Say that we want to use JWT. The first 2 values came straight from the Contoso7 metadata document.
You can see highlighted in red the issuer value, in blue the audience, and in green the relevant claims used to assess whether the token is expired. Currently we offer various ways for you to inject validation logic in front of your application. You can choose to work directly with the JWT token handler class, as shown hereand configure it to use the above values as validation parameters. You can choose to use the OWIN middleware, as shown herewhich makes your job much easier but gives less control.
The key point is, ultimately all those techniques will perform the checks described above. The above contains a lot of simplifications, and does not really give any details about another crucial component which requires configuration, the protocol parts — however it provides me with a base I can use to explain more complicated scenarios like this one — which is going to be so much easier with the new Owin components.
The future is token verification here - simply, it is not very evenly distributed.
Fix that by sharing!