8:18 p.m.
Hey guys,
I've completed the first round of redesigns for the credentials API
based on the feedback provided by Darran and others. It might require
some minimal tweaking to address a couple of minor edge cases, however
at this point in time I'd like to run through the basic design to see
what you guys think. Up front I must say that it's more complex than I
had hoped, however after analysing all the use cases I feel that the
complexity is a necessity for providing a truly robust, extensible API.
To try and present this in a logical manner, I'm going to describe the
credentials API in terms of the chronological order of events during the
authentication process. To start with, let's take a look at the
LoginCredentials interface:
public interface LoginCredentials {
void invalidate();
}
Implementations of this interface are intended to contain the state
provided by the user in order to carry out authentication. While the
Credential interface is designed to represent an atomic credential value
(such as a password, certificate, or biometric data such as a
fingerprint), LoginCredentials is designed to encapsulate the credential
value with additional state required by the authentication process.
Let's take a look at an implementation supporting the most common form
of credentials, a username and password:
public class UsernamePasswordCredentials implements LoginCredentials {
private String username;
private PasswordCredential password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public PasswordCredential getPassword() {
return password;
}
public void setPassword(PasswordCredential password) {
this.password = password;
}
@Override
public void invalidate() {
username = null;
password.clear();
}
}
This implementation provides the capability for setting a username
(represented as a String) and a PasswordCredential. Other
implementations are free to define whichever properties they require,
for example a CertificateCredentials class may simply contain an
X509CertificateCredential and nothing else.
Once the user provides their credentials, the LoginCredentials instance
can be passed to IdentityManager via the following method:
public interface IdentityManager {
User validateCredentials(LoginCredentials credentials);
}
To handle the actual processing of the credentials and perform whatever
business logic is required to authenticate the user, the following SPI
interface is used:
public interface CredentialHandler {
User validate(LoginCredentials credentials, IdentityStore store);
void update(User user, Credential credential, IdentityStore store);
}
Since authentication is handled differently depending on what type of
IdentityStore is being used, there will be many CredentialHandler
implementations to address each use case combination. To determine the
correct CredentialHandler implementation to use for authentication, the
IdentityManager calls CredentialHandlerFactory.getCredentialHandler(),
passing in the class of the LoginCredentials parameter and the class of
the IdentityStore parameter:
public interface CredentialHandlerFactory {
CredentialHandler getCredentialHandler(Class<? extends
LoginCredentials> credentialsClass,
Class<? extends IdentityStore> identityStoreClass);
}
This allows us to provide a separate CredentialHandler implementation
for each combination of LoginCredentials and IdentityStore. For
example, for a standard username/password authentication using
JPAIdentityStore we may have a JPAUsernamePasswordCredentialHandler that
compares a calculated hash based on the password (and possible other
values) against a pre-calculated hash stored in the database. For a
username/password authentication against LDAPIdentityStore we may have
an LDAPUsernamePasswordCredentialHandler that performs a bind operation
against the directory to ensure that the credentials supplied are
valid. As the SPI is extensible, it is also possible for developers to
provide their own CredentialHandler implementations to suit whichever
authentication process they require.
If the CredentialHandler.validate() method completes successfully, it is
expected to return a User instance to indicate that authentication was
successful. If authentication is unsuccessful (or possibly requires
multiple steps) then it's up to the caller and implementation to cater
for this, most likely by providing additional state within the
LoginCredentials implementation.
To sidetrack for a moment, the CredentialHandlerFactory is configured as
part of the IdentityConfiguration which is passed to the
IdentityManager's bootstrap method during startup:
public class IdentityConfiguration {
public CredentialHandlerFactory getCredentialHandlerFactory() {
return credentialHandlerFactory;
}
public void setCredentialHandlerFactory(CredentialHandlerFactory
factory) {
this.credentialHandlerFactory = factory;
}
}
Continuing on, the CredentialHandler is free to execute whichever
business logic is required to authenticate the provided LoginCredentials
value. It has direct access to the IdentityStore instance, in which the
previous credential management methods have been replaced with the
following two new methods (side note - the CredentialHandler doesn't
*have* to use these methods, it could instead possibly invoke other
IdentityStore methods by casting the IdentityStore to the appropriate type):
public interface IdentityStore {
void storeCredential(CredentialStorage storage);
CredentialStorage retrieveCredential(Class<? extends
CredentialStorage> storageClass);
}
At present CredentialStorage is a simple SPI interface that declares a
single method:
public interface CredentialStorage {
Date getExpiryDate();
}
The reason that we have introduced a totally new interface here rather
than just use the Credential interface, is that credential information
stored by the IdentityStore is often different to the credential
information provided by a user to authenticate. For example, in
username/password authentication the user provides a plain text
password, however the data we have stored in the IdentityStore is
typically not the password itself, but a hash value (or at least I would
hope so). With that in mind, the introduction of the CredentialStorage
interface formalizes the disconnect between user-provided credential
state and stored credential state, and in turn provides a more flexible
design. This is not to say that a Credential implementation can't be
dual purpose, in fact this is fully supported thanks to
CredentialStorage essentially being a marker interface, so
X509CertificateCredential for example could easily implement both the
Credential and CredentialStorage interfaces.
To round this off with a solid example, here's what a CredentialStorage
implementation that stores a password hash might look like:
public class PasswordHash implements CredentialStorage {
private byte[] hash;
public void setHash(byte[] hash) {
this.hash = hash;
}
public byte[] getHash() {
return hash;
}
}
There's actually one more step here, and that's the metadata required by
the IdentityStore to know which state of the CredentialStorage instance
to actually store. To enable this, we have introduced the @Stored
annotation, which when added to the above example looks like this:
public class PasswordHash implements CredentialStorage {
@Stored private byte[] hash;
public void setHash(byte[] hash) {
this.hash = hash;
}
public byte[] getHash() {
return hash;
}
}
Any properties annotated with @Stored must be Serializable, to allow
storage by the IdentityStore.
One last thing that needs to be covered is the updating of credentials.
IdentityManager also provides this method which is used to update a
user's credentials:
public interface IdentityManager {
void updateCredential(User user, Credential credential);
}
Like credential validation, a CredentialHandler is looked up the same
way and its update() method is invoked with the User, Credential and
IdentityStore parameters. It is up to the CredentialHandler
implementation to create the appropriate CredentialStorage instances (or
perform whichever other business logic that might be required) to
persist to the backend IdentityStore.
That pretty much covers everything. I think this design in essences
addresses all of the use cases discussed so far, and should be
relatively future-proof. Sorry again for another wall of text, but I'm
looking forward to hearing feedback on this. There's still quite a lot
of work to do in this area on the implementation side of things (such as
decoupling the existing credential validation code from the
IdentityStore implementations and implementing it as CredentialHandlers)
but we'll get to that once everyone has a chance to review this new design.
Thanks,
Shane