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Authentication in Backstage

The authentication system in Backstage serves two distinct purposes: sign-in and identification of users, as well as delegating access to third-party resources. It is possible to configure Backstage to have any number of authentication providers, but only one of these will typically be used for sign-in, with the rest being used to provide access to external resources.

Note

Identity management and the Sign-In page in Backstage will only block external access when using the new backend system, without setting backend.auth.dangerouslyDisableDefaultAuthPolicy in configuration. Even so, the frontend bundle is not protected from external access, protecting it requires the use of the experimental public entry point. You can learn more about this in the Threat Model.

Built-in Authentication Providers​

Backstage comes with many common authentication providers in the core library:

These built-in providers handle the authentication flow for a particular service, including required scopes, callbacks, etc. These providers are each added to a Backstage app in a similar way.

Configuring Authentication Providers​

Each built-in provider has a configuration block under the auth section of app-config.yaml. For example, the GitHub provider:

auth:
  environment: development
  providers:
    github:
      development:
        clientId: ${AUTH_GITHUB_CLIENT_ID}
        clientSecret: ${AUTH_GITHUB_CLIENT_SECRET}

See the documentation for a particular provider to see what configuration is needed.

The providers key may have several authentication providers if multiple authentication methods are supported. Each provider may also have configuration for different authentication environments (development, production, etc). This allows a single auth backend to serve multiple environments, such as running a local frontend against a deployed backend. The provider configuration matching the local auth.environment setting will be selected.

Sign-In Configuration​

Using an authentication provider for sign-in is something you need to configure both in the frontend app as well as the auth backend plugin. For information on how to configure the backend app, see Sign-in Identities and Resolvers. The rest of this section will focus on how to configure sign-in for the frontend app.

Sign-in is configured by providing a custom SignInPage app component. It will be rendered before any other routes in the app and is responsible for providing the identity of the current user. The SignInPage can render any number of pages and components, or just blank space with logic running in the background. In the end, however, it must provide a valid Backstage user identity through the onSignInSuccess callback prop, at which point the rest of the app is rendered.

If you want to, you can use the SignInPage component that is provided by @backstage/core-components, which takes either a provider or providers (array) prop of SignInProviderConfig definitions.

The following example for GitHub shows the additions needed to packages/app/src/App.tsx, and can be adapted to any of the built-in providers:

packages/app/src/App.tsx
import { githubAuthApiRef } from '@backstage/core-plugin-api';
import { SignInPage } from '@backstage/core-components';

const app = createApp({
  components: {
    SignInPage: props => (
      <SignInPage
        {...props}
        auto
        provider={{
          id: 'github-auth-provider',
          title: 'GitHub',
          message: 'Sign in using GitHub',
          apiRef: githubAuthApiRef,
        }}
      />
    ),
  },
  // ..
});
Note

You can configure sign-in to use a redirect flow with no pop-up by adding enableExperimentalRedirectFlow: true to the root of your app-config.yaml

Using Multiple Providers​

You can also use the providers prop to enable multiple sign-in methods, for example to allow guest access:

packages/app/src/App.tsx
const app = createApp({
  components: {
    SignInPage: props => (
      <SignInPage
        {...props}
        providers={[
          'guest',
          {
            id: 'github-auth-provider',
            title: 'GitHub',
            message: 'Sign in using GitHub',
            apiRef: githubAuthApiRef,
          },
        ]}
      />
    ),
  },
  // ..
});

Conditionally Render Sign In Provider​

In the above example, you have both Guest and GitHub sign-in options; this is helpful for non-production, but in Production you will most likely not want to offer Guest access. You can easily use information from your config to help conditionally render the provider:

packages/app/src/App.tsx
import {
  configApiRef,
  githubAuthApiRef,
  useApi,
} from '@backstage/core-plugin-api';

const app = createApp({
  components: {
    SignInPage: props => {
      const configApi = useApi(configApiRef);
      if (configApi.getString('auth.environment') === 'development') {
        return (
          <SignInPage
            {...props}
            providers={[
              'guest',
              {
                id: 'github-auth-provider',
                title: 'GitHub',
                message: 'Sign in using GitHub',
                apiRef: githubAuthApiRef,
              },
            ]}
          />
        );
      }
      return (
        <SignInPage
          {...props}
          provider={{
            id: 'google-auth-provider',
            title: 'Google',
            message: 'Sign In using Google',
            apiRef: googleAuthApiRef,
          }}
        />
      );
    },
  },
  // ..
});

Sign-In with Proxy Providers​

Some auth providers are so-called "proxy" providers, meaning they're meant to be used behind an authentication proxy. Examples of these are Amazon Application Load Balancer, Azure EasyAuth, Cloudflare Access, Google Identity-Aware Proxy and OAuth2 Proxy.

When using a proxy provider, you'll end up wanting to use a different sign-in page, as there is no need for further user interaction once you've signed in towards the proxy. All the sign-in page needs to do is call the /refresh endpoint of the auth providers to get the existing session, which is exactly what the ProxiedSignInPage does. The only thing you need to do to configure the ProxiedSignInPage is to pass the ID of the provider like this:

packages/app/src/App.tsx
const app = createApp({
  components: {
    SignInPage: props => <ProxiedSignInPage {...props} provider="awsalb" />,
  },
  // ..
});

If the provider in auth backend expects additional headers such as x-provider-token, there is now a way to configure that in ProxiedSignInPage using the optional headers prop.

Example:

<ProxiedSignInPage
  {...props}
  provider="my-custom-provider"
  headers={{ 'x-some-key': someValue }}
/>

Headers can also be returned in an async manner:

<ProxiedSignInPage
  {...props}
  provider="my-custom-provider"
  headers={async () => {
    const someValue = await someFn();
    return { 'x-some-key': someValue };
  }}
/>

A downside of this method is that it can be cumbersome to set up for local development. As a workaround for this, it's possible to dynamically select the sign-in page based on what environment the app is running in and then use a different sign-in method for local development, if one is needed at all. Depending on the exact setup, one might choose to select the sign-in method based on the process.env.NODE_ENV environment variable, by checking the hostname of the current location, or by accessing the configuration API to read a configuration value. For example:

packages/app/src/App.tsx
const app = createApp({
  components: {
    SignInPage: props => {
      const configApi = useApi(configApiRef);
      if (configApi.getString('auth.environment') === 'development') {
        return (
          <SignInPage
            {...props}
            provider={{
              id: 'google-auth-provider',
              title: 'Google',
              message: 'Sign In using Google',
              apiRef: googleAuthApiRef,
            }}
          />
        );
      }
      return <ProxiedSignInPage {...props} provider="gcpiap" />;
    },
  },
  // ..
});

When using multiple auth providers like this, it's important that you configure the different sign-in resolvers so that they resolve to the same identity regardless of the method used.

Scaffolder Configuration (Software Templates)​

If you want to use the authentication capabilities of the Repository Picker inside your software templates, you will need to configure the ScmAuthApi alongside your authentication provider. It is an API used to authenticate towards different SCM systems in a generic way, based on what resource is being accessed.

To set it up, you'll need to add an API factory entry to packages/app/src/apis.ts. The example below sets up the ScmAuthApi for an already configured GitLab authentication provider:

packages/app/src/apis.ts
createApiFactory({
  api: scmAuthApiRef,
  deps: {
    gitlabAuthApi: gitlabAuthApiRef,
  },
  factory: ({ gitlabAuthApi }) => ScmAuth.forGitlab(gitlabAuthApi),
});

In case you are using a custom authentication providers, you might need to add a custom ScmAuthApi implementation.

For Plugin Developers​

The Backstage frontend core APIs provide a set of Utility APIs for plugin developers to use, both to access the user identity as well as third-party resources.

Identity for Plugin Developers​

For plugin developers, there is one main touchpoint for accessing the user identity: the IdentityApi exported by @backstage/core-plugin-api via the identityApiRef.

The IdentityApi gives access to the signed-in user's identity in the frontend. It provides access to the user's entity reference, lightweight profile information, and a Backstage token that identifies the user when making authenticated calls within Backstage.

When making calls to backend plugins, we recommend that the FetchApi is used, which is exported via the fetchApiRef from @backstage/core-plugin-api. The FetchApi will automatically include a Backstage token in the request, meaning there is no need to interact directly with the IdentityApi.

Accessing Third Party Resources​

A common pattern for talking to third-party services in Backstage is user-to-server requests, where short-lived OAuth Access Tokens are requested by plugins to authenticate calls to external services. These calls can be made either directly to the services or through a backend plugin or service.

By relying on user-to-server calls, we keep the coupling between the frontend and backend low and provide a much lower barrier for plugins to make use of third party services. This is in comparison to, for example, a session-based system where access tokens are stored server-side. Such a solution would require a much deeper coupling between the auth backend plugin, its session storage, and other backend plugins or separate services. A goal of Backstage is to make it as easy as possible to create new plugins, and an auth solution based on user-to-server OAuth helps in that regard.

The method with which frontend plugins request access to third-party services is through Utility APIs for each service provider. These are all suffixed with *AuthApiRef, for example githubAuthApiRef. For a full list of providers, see the @backstage/core-plugin-api reference.

Custom Authentication Provider​

There are generic authentication providers for OAuth2 and SAML. These can reduce the amount of code needed to implement a custom authentication provider that adheres to these standards.

Backstage uses Passport under the hood, which has a wide library of authentication strategies for different providers. See Add authentication provider for details on adding a new Passport-supported authentication method.

Custom ScmAuthApi Implementation​

The default ScmAuthApi provides integrations for github, gitlab, azure and bitbucket and is created by the following code in packages/app/src/apis.ts:

ScmAuth.createDefaultApiFactory();

If you require only a subset of these integrations, then you will need a custom implementation of the ScmAuthApi. It is an API used to authenticate different SCM systems generically, based on what resource is being accessed, and is used for example, by the Scaffolder (Software Templates) and Catalog Import plugins.

The first step is to remove the code that creates the default providers.

packages/app/src/apis.ts
import {
  ScmIntegrationsApi,
  scmIntegrationsApiRef,
  ScmAuth,
} from '@backstage/integration-react';

export const apis: AnyApiFactory[] = [
  ScmAuth.createDefaultApiFactory(),
  // ...
];

Then replace it with something like this, which will create an ApiFactory with only a GitHub provider.

packages/app/src/apis.ts
export const apis: AnyApiFactory[] = [
  createApiFactory({
    api: scmAuthApiRef,
    deps: {
      githubAuthApi: githubAuthApiRef,
    },
    factory: ({ githubAuthApi }) =>
      ScmAuth.merge(
        ScmAuth.forGithub(githubAuthApi),
      ),
  });

If you use any custom authentication integrations, a new provider can be added to the ApiFactory.

The first step is to create a new authentication ref, which follows the naming convention of xxxAuthApiRef. The example below is for a new GitHub enterprise integration which can be defined either inside the app itself if it's only used for this purpose or inside a common internal package for APIs, such as @internal/apis:

const gheAuthApiRef: ApiRef<OAuthApi & ProfileInfoApi & SessionApi> =
  createApiRef({
    id: 'internal.auth.ghe',
  });

This new API ref will only work if you define an API factory for it. For example:

createApiFactory({
  api: gheAuthApiRef,
  deps: {
    discoveryApi: discoveryApiRef,
    oauthRequestApi: oauthRequestApiRef,
    configApi: configApiRef,
  },
  factory: ({ discoveryApi, oauthRequestApi, configApi }) =>
    GithubAuth.create({
      configApi,
      discoveryApi,
      oauthRequestApi,
      provider: { id: 'ghe', title: 'GitHub Enterprise', icon: () => null },
      defaultScopes: ['read:user'],
      environment: configApi.getOptionalString('auth.environment'),
    }),
});

The new API ref is then used to add a new provider to the ApiFactory:

createApiFactory({
  api: scmAuthApiRef,
  deps: {
    gheAuthApi: gheAuthApiRef,
    githubAuthApi: githubAuthApiRef,
  },
  factory: ({ githubAuthApi, gheAuthApi }) =>
    ScmAuth.merge(
      ScmAuth.forGithub(githubAuthApi),
      ScmAuth.forGithub(gheAuthApi, {
        host: 'ghe.example.com',
      }),
    ),
});

Finally, you also need to add and configure another provider to the auth-backend using the provider ID, which in this example is ghe:

import { providers } from '@backstage/plugin-auth-backend';

// Add the following options to `createRouter` in packages/backend/src/plugins/auth.ts
providerFactories: {
  ghe: providers.github.create(),
},

Configuring token issuers​

By default, the Backstage authentication backend generates and manages its own signing keys automatically for any issued Backstage tokens. However, these keys have a short lifetime and do not persist after instance restarts.

Alternatively, users can provide their own public and private key files to sign issued tokens. This is beneficial in scenarios where the token verification implementation aggressively caches the list of keys, and doesn't attempt to fetch new ones even if they encounter an unknown key id. To enable this feature add the following configuration to your config file:

auth:
  keyStore:
    provider: 'static'
    static:
      keys:
        # Must be declared at least once and the first one will be used for signing
        - keyId: 'primary'
          publicKeyFile: /path/to/public.key
          privateKeyFile: /path/to/private.key
          algorithm: # Optional, algorithm used to generate the keys, defaults to ES256
          # More keys can be added so with future key rotations caches already know about it
        - keyId: ...

The private key should be stored in the PKCS#8 format. The public key should be stored in the SPKI format. You can generate the public/private key pair, using openssl and the ES256 algorithm by performing the following steps:

Generate a private key using the ES256 algorithm

openssl ecparam -name prime256v1 -genkey -out private.ec.key

Convert it to PKCS#8 format

openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in private.ec.key -out private.key

Extract the public key

openssl ec -inform PEM -outform PEM -pubout -in private.key -out public.key