CredHub API Client

CredHub manages credentials, such as passwords, certificates, certificate authorities, ssh keys, RSA keys, and other arbitrary values. Steeltoe provides the CredHubBase library for interacting with the CredHub API and provides the CredHubCore library for making that client library simpler to use in ASP.NET Core applications. Cloud Foundry is not required for the CredHub server or client but is used in this documentation as the hosting environment. You may wish to review the documentation for CredHub on PCF. If you do not already have a UAA user to use for this test, you need to use the UAA command-line tool to establish some security credentials for the sample application. Choose one of the provided credhub-setup scripts in the folder samples/Security/scripts to target your Cloud Foundry environment and create a UAA client with permissions to read and write in CredHub.

If you choose to change the values for UAA_CLIENT_ID or UAA_CLIENT_SECRET, be sure to update the credentials in appsettings.json.

WARNING: As of this writing, CredHub is not approved for general use in all applications. We encourage you to check whether your use case is currently supported by CredHub before getting too involved.

Usage

To use the Steeltoe CredHub client, you must:

• Have access to a CredHub Server (the client was built against version 1.6.5)
• Have UAA credentials for accessing the server with sufficient permissions for your use case
• Use the provided methods and constructors to create, inject, or use the client

Add NuGet Reference

To use this library with ASP.NET Core, add a NuGet reference to Steeltoe.Security.DataProtection.CredHubCore. For other application types, use Steeltoe.Security.DataProtection.CredHubBase. Most of the functionality resides in CredHubBase. The purpose of CredHubCore is to provide additional methods for a simpler experience when using ASP.NET Core.

Use the NuGet package manager tools or directly add the appropriate package to your project using the a PackageReference, as follows:

<ItemGroup>
...
    <PackageReference Include="Steeltoe.Security.DataProtection.CredHubCore" Version="3.2.0"/>
...
</ItemGroup>

Configure Settings

Settings for this library are expected to have a prefix of CredHubClient. The following example shows what that looks like in JSON:

{
  ...
  "CredHubClient": {
    "ValidateCertificates": "false"
  }
  ...
}

The CredHubClient supports four settings:

Key	Description	Default
CredHubUrl	The address of the CredHub API.	https://credhub.service.cf.internal:8844/api
CredHubUser	The username for UAA auth.	null
CredHubPassword	The password for UAA auth.	null
ValidateCertificates	Whether to validate certificates for UAA and/or CredHub servers.	true

The samples and most templates are already set up to read from appsettings.json.

On Cloud Foundry

TAS (in versions 2.0 and up) ships with a version of CredHub Server with which this client works. To use UAA authentication, you need a user with credhub.read or credhub.write claims.

Getting a Client

There are several ways to create a CredHubClient, depending on whether you want to use Microsoft's dependency injection. Regardless of the creation method selected, once the client has been created, all functionality is the same.

Create and Inject Client

If you use Microsoft's dependency injection framework, you can use IServiceCollection.AddCredHubClient() to create, configure, and inject CredHubClient:

using Steeltoe.Security.DataProtection.CredHubCore;
...
public class Startup
{
    ILoggerFactory logFactory;
    public Startup(IConfiguration configuration, ILoggerFactory logFactory)
    {
        Configuration = configuration;
        this.logFactory = logFactory;
    }
    public IConfiguration Configuration { get; }
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
        services.AddCredHubClient(Configuration, logFactory);
    }
    ...
}
...

Create UAA Client

You can use CredHubClient.CreateUAAClientAsync() to directly create a CredHub client that authenticates with a username and password that is valid on the UAA server that CredHub is configured to trust. This client calls /info on the CredHub server to discover the UAA server's address and appends /oauth/token when requesting a token. The following listing shows how to do it:

var credHubClient = await CredHubClient.CreateUAAClientAsync(new CredHubOptions());

If you need to override the UAA server address, use the UAA_Server_Override environment variable, making sure to include the path to the token endpoint.

Interpolation-Only

If you wish to use CredHub to interpolate entries in VCAP_SERVICES, you can use WebHostBuilder.UseCredHubInterpolation(). This method looks for credhub-ref in VCAP_SERVICES and uses a CredHubClient to replace the credential references with credentials stored in CredHub but does not return the CredHubClient. The following example shows how to do it:

    var host = new WebHostBuilder()
        .UseKestrel()
        .UseCloudHosting()
        .UseContentRoot(Directory.GetCurrentDirectory())
        .UseIISIntegration()
        .UseStartup<Startup>()
        .ConfigureAppConfiguration((builderContext, config) =>
        {
            config.SetBasePath(builderContext.HostingEnvironment.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{builderContext.HostingEnvironment.EnvironmentName}.json", optional: true)
                .AddCloudFoundry()
                .AddEnvironmentVariables();
        })
        .ConfigureLogging((builderContext, loggingBuilder) =>
        {
            loggingBuilder.AddConfiguration(builderContext.Configuration.GetSection("Logging"));
            loggingBuilder.AddDynamicConsole();
        })
        .UseCredHubInterpolation(new LoggerFactory().AddConsole())
        .Build();

Credential Types

These are the .NET representations of credentials that can be stored in CredHub. See the CredHub documentation for more detail.

ValueCredential

Any string can be used for a ValueCredential. CredHub allows get, set, delete, and find operations with ValueCredential.

PasswordCredential

Any string can be used for a PasswordCredential. CredHub allows get, set, delete, find, generate, and regenerate operations with PasswordCredential.

UserCredential

A UserCredential has string properties for Username and Password. CredHub allows get, set, delete, find, generate, and regenerate operations with UserCredential. Regenerate operations do not regenerate the username.

JsonCredential

You can use any JSON object for a JsonCredential. CredHub allows get, set, delete, and find operations with JsonCredential.

CertificateCredential

A CertificateCredential represents a security certificate. CredHub allows get, set, delete, find, generate, regenerate, and bulk regenerate operations with CertificateCredential. The following table describes specific properties:

Key	Description
CertificateAuthority	The certificate of the Certificate Authority.
CertificateAuthorityName	The name of the CA credential in CredHub that has signed this certificate.
Certificate	The string representation of the certificate.
PrivateKey	The private key for the certificate.

RsaCredential

The RsaCredential has string properties for PublicKey and PrivateKey. CredHub allows get, set, delete, find, generate, and regenerate operations with RsaCredential.

SshCredential

The SshCredential has string properties for PublicKey, PrivateKey, and PublicKeyFingerprint. CredHub allows get, set, delete, find, generate, and regenerate operations with SshCredential.

CredHub Read Operations

All CredHubClient read operations operate asynchronously and do not change the credentials or permissions stored in CredHub. See the CredHub documentation for more detail. For brevity, the samples shown later in this guide use _credHubClient to reference an instance of CredHubClient that has been created previously.

Get by ID

You can use await _credHubClient.GetByIdAsync<CredentialType>(credentialId) to retrieve a credential by its Guid. Only the current credential value is returned.

Get by Name

You can use await _credHubClient.GetByNameAsync<CredentialType>(credentialName) to retrieve a credential by its Name. Only the current credential value is returned.

Get by Name with History

You can use await _credHubClient.GetByNameWithHistoryAsync<CredentialType>(credentialName, numEntries) to retrieve a credential by name, with the most recent numEntries holding the number of entries.

Find by Name

You can use await _credHubClient.FindByNameAsync(credentialName) to retrieve a list of FoundCredential objects that are either a full or partial match for the name searched. The FoundCredential type includes only the Name and VersionCreatedAt properties, so follow-up requests are expected to retrieve credential details.

Find by Path

You can use await _credHubClient.FindByPathAsync(path) to retrieve a list of FoundCredential objects that are either a full or partial match for the name searched. The FoundCredential type includes only the Name and VersionCreatedAt properties, so you need to use follow-up requests to retrieve credential details. Use the / path value to return all accessible credentials.

Find All Paths

You can use await _credHub.FindAllPathsAsync() to retrieve a list of all known credential paths.

Interpolate

One of the more powerful features of CredHub is the Interpolate endpoint. With one request, you may retrieve N number of credentials that have been stored in CredHub. To use it from .NET, call await _credHub.InterpolateServiceDataAsync(serviceData), where serviceData is the string representation of VCAP_SERVICES. CredHubClient returns the interpolated VCAP_SERVICES data as a string.

The following example shows a typical request object for the Interpolate endpoint:

{
  "p-demo-resource": [
    {
      "credentials": {
        "credhub-ref": "((/config-server/credentials))"
      },
      "label": "p-config-server",
      "Name": "config-server",
      "plan": "standard",
      "provider": null,
      "syslog_drain_url": null,
      "tags": [
        "configuration",
        "spring-cloud"
      ],
      "volume_mounts": []
    }
  ]
}

The following example shows a typical response object from the Interpolate endpoint:

{
  "p-demo-resource": [
    {
      "credentials": {
        "key": 123,
        "key_list": [
          "val1",
          "val2"
        ],
        "is_true": true
      },
      "label": "p-config-server",
      "Name": "config-server",
      "plan": "standard",
      "provider": null,
      "syslog_drain_url": null,
      "tags": [
        "configuration",
        "spring-cloud"
      ],
      "volume_mounts": []
    }
  ]
}

At this time, only credential references at credentials.credhub-ref are interpolated. The credhub-ref key is removed, and the referenced credential object is set as the value of the credentials.

CredHub Change Operations

All CredHubClient change operations operate asynchronously and affect stored credentials. See the CredHub documentation for more detail. For brevity, the samples shown later in this guide use _credHubClient to reference an instance of CredHubClient that has been created previously.

Write

If you already have a credential that you want to store in CredHub, use a Write request. CredHubClient.WriteAsync<T>() expects a request object that descends from CredentialSetRequest. There is a [Type]SetRequest class for each credential type (ValueSetRequest, PasswordSetRequest, and so on). The *SetRequest family of classes includes optional parameters for overwriting existing values and setting permissions, in addition to value properties for the credential. Include the type of credential you want to write to CredHub in the T parameter so that the compiler knows the return type. The following example shows a typical Write request:

var setValueRequest = new ValueSetRequest("sampleValueCredential", "someValue");
// set the value of credential "/sampleValueCredential" to "someValue" if there is NOT an existing value
var setValue1 = await _credHub.WriteAsync<ValueCredential>(setValueRequest);

// set the value of credential "/sampleValueCredential" to "someValue" even if there is an existing value
setValueRequest.Overwrite = true;
var setValue2 = await _credHub.WriteAsync<ValueCredential>(setValueRequest);

The default behavior on Write requests is to leave existing values alone. If you wish to overwrite a credential, be sure to pass either OverwriteMode.converge or OverwriteMode.overwrite for the overwriteMode parameter on your request object. See Overwriting Credential Values.

Write requests allow the setting of permissions on a credential during generation, as follows:

var desiredOperations = new List<OperationPermissions>
                        {
                            OperationPermissions.read,
                            OperationPermissions.write,
                            OperationPermissions.delete
                        };
var newPerms = new CredentialPermission { Actor = "uaa-user:credhub_client", Operations = desiredOperations };
var setRequest = new ValueSetRequest("sampleValueCredential", "someValue", new List<CredentialPermission> { newPerms });
var setValue = await _credHub.WriteAsync<ValueCredential>(setRequest);

Generate

You can generate a new credential or overwrite an existing credential with a new generated value. CredHub is able to generate values for the following types: CertificateCredential, PasswordCredential, RsaCredential, SshCredential, and UserCredential. CredHubClient.GenerateAsync<T>() expects a request object that descends from CredHubGenerateRequest. There is a [Type]GenerateRequest class for each supported credential type (CertificateGenerationRequest, PasswordGenerationRequest, RsaGenerationRequest, and so on). Most of the *GenerateRequest family of classes include a [Type]GenerationParameters parameter for specifying criteria to be used when generating the credential. The following example shows how to generate a credential:

var genParameters = new PasswordGenerationParameters { Length = 20 };
var genRequest = new PasswordGenerationRequest("generatedPassword", genParameters);
CredHubCredential<PasswordCredential> genPassword = await _credHub.GenerateAsync<PasswordCredential>(genRequest);

The following example demonstrates that Generate requests allow the setting of permissions on a credential during generation:

var genParams = new PasswordGenerationParameters { Length = 20 };
var desiredOperations = new List<OperationPermissions>
                        {
                            OperationPermissions.read,
                            OperationPermissions.write,
                            OperationPermissions.delete
                        };
var newPerms = new CredentialPermission { Actor = "uaa-user:credhub_client", Operations = desiredOperations };
var genRequest = new PasswordGenerationRequest("generatedPW", genParams, new List<CredentialPermission> { newPerms });
CredHubCredential<PasswordCredential> genPassword = await _credHub.GenerateAsync<PasswordCredential>(genRequest);

The default behavior on Generate requests is to leave existing values alone. If you wish to overwrite a credential, be sure to pass either OverwriteMode.converge or OverwriteMode.overwrite for the overwriteMode parameter on your request object. See Overwriting Credential Values.

Regenerate

You can regenerate a credential in CredHub. CredHub can generate values for the following types: CertificateCredential, PasswordCredential, RsaCredential, SshCredential, and UserCredential.

Only credentials that were previously generated by CredHub can be regenerated.

The following example shows one way to regenerate a credential:

var regeneratedCert = await _credHub.RegenerateAsync<CertificateCredential>("/MyGeneratedCert");

Bulk Regenerate

You can regenerate all certificates that were previously generated by CredHub with a given certificate authority. The following example returns a list of RegeneratedCertificates that contains the credential names as a List<string> property named bulkRegenerate:

RegeneratedCertificates bulkRegenerate = await _credHub.BulkRegenerateAsync("NameThatCA");

Delete by Name

You can delete a credential by its full name. The following example returns a boolean indicating success or failure:

bool deleteCertificate = await _credHub.DeleteByNameAsync("/MyPreviouslyGeneratedCertificate");

Permission Operations

CredHub supports permissions management on credential access for UAA users. See the official CredHub permissions documentation.

Get Permissions

You can get the permissions associated with a credential, as follows:

List<CredentialPermission> response = await _credHub.GetPermissionsAsync("/example-password");

Add Permissions

You can add permissions to an existing credential. The following example returns the updated list of permissions for the specified credential:

var desiredOps = new List<OperationPermissions> { OperationPermissions.read, OperationPermissions.write };
var newActorPermissions = new CredentialPermission { Actor = "uaa-user:credhub_client", Operations = desiredOps };
var newPerms = new List<CredentialPermission> { newActorPermissions };
List<CredentialPermission> response = await _credHub.AddPermissionsAsync("/example-password", newPerms);

Delete Permissions

You can delete the permission associated with a credential. The following example returns a boolean indicating success or failure:

bool response = await _credHub.DeletePermissionAsync("/example-password", "uaa-user:credhub_client");