Create username scope, required for clients to get username in ID token

- For backwards compatibility with older Pinniped CLIs, the pinniped-cli
  client does not need to request the username or groups scopes for them
  to be granted. For dynamic clients, the usual OAuth2 rules apply:
  the client must be allowed to request the scopes according to its
  configuration, and the client must actually request the scopes in the
  authorization request.
- If the username scope was not granted, then there will be no username
  in the ID token, and the cluster-scoped token exchange will fail since
  there would be no username in the resulting cluster-scoped ID token.
- The OIDC well-known discovery endpoint lists the username and groups
  scopes in the scopes_supported list, and lists the username and groups
  claims in the claims_supported list.
- Add username and groups scopes to the default list of scopes
  put into kubeconfig files by "pinniped get kubeconfig" CLI command,
  and the default list of scopes used by "pinniped login oidc" when
  no list of scopes is specified in the kubeconfig file
- The warning header about group memberships changing during upstream
  refresh will only be sent to the pinniped-cli client, since it is
  only intended for kubectl and it could leak the username to the
  client (which may not have the username scope granted) through the
  warning message text.
- Add the user's username to the session storage as a new field, so that
  during upstream refresh we can compare the original username from the
  initial authorization to the refreshed username, even in the case when
  the username scope was not granted (and therefore the username is not
  stored in the ID token claims of the session storage)
- Bump the Supervisor session storage format version from 2 to 3
  due to the username field being added to the session struct
- Extract commonly used string constants related to OIDC flows to api
  package.
- Change some import names to make them consistent:
  - Always import github.com/coreos/go-oidc/v3/oidc as "coreosoidc"
  - Always import go.pinniped.dev/generated/latest/apis/supervisor/oidc
    as "oidcapi"
  - Always import go.pinniped.dev/internal/oidc as "oidc"

internal/testutil/oidcclient.go

@@ -7,6 +7,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/stretchr/testify/require"
+	"golang.org/x/crypto/bcrypt"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
@@ -41,19 +43,30 @@ func allDynamicClientScopes() []configv1alpha1.Scope {
 	return scopes
 }
 
-// fullyCapableOIDCClient returns an OIDC client which is allowed to use all grant types and all scopes that
-// are supported by the Supervisor for dynamic clients.
-func fullyCapableOIDCClient(namespace string, clientID string, clientUID string, redirectURI string) *configv1alpha1.OIDCClient {
+func newOIDCClient(
+	namespace string,
+	clientID string,
+	clientUID string,
+	redirectURI string,
+	allowedGrantTypes []configv1alpha1.GrantType,
+	allowedScopes []configv1alpha1.Scope,
+) *configv1alpha1.OIDCClient {
 	return &configv1alpha1.OIDCClient{
 		ObjectMeta: metav1.ObjectMeta{Namespace: namespace, Name: clientID, Generation: 1, UID: types.UID(clientUID)},
 		Spec: configv1alpha1.OIDCClientSpec{
-			AllowedGrantTypes:   []configv1alpha1.GrantType{"authorization_code", "urn:ietf:params:oauth:grant-type:token-exchange", "refresh_token"},
-			AllowedScopes:       allDynamicClientScopes(),
+			AllowedGrantTypes:   allowedGrantTypes,
+			AllowedScopes:       allowedScopes,
 			AllowedRedirectURIs: []configv1alpha1.RedirectURI{configv1alpha1.RedirectURI(redirectURI)},
 		},
 	}
 }
 
+// OIDCClientValidatorFunc is an interface-like type that allows these test helpers to avoid having a direct dependency
+// on the production code, to avoid circular module dependencies. Implemented by oidcclientvalidator.Validate.
+type OIDCClientValidatorFunc func(oidcClient *configv1alpha1.OIDCClient, secret *corev1.Secret, minBcryptCost int) (bool, []*configv1alpha1.Condition, []string)
+
+// FullyCapableOIDCClientAndStorageSecret returns an OIDC client which is allowed to use all grant types and all scopes
+// that are supported by the Supervisor for dynamic clients, along with a corresponding client secret storage Secret.
 func FullyCapableOIDCClientAndStorageSecret(
 	t *testing.T,
 	namespace string,
@@ -61,7 +74,38 @@ func FullyCapableOIDCClientAndStorageSecret(
 	clientUID string,
 	redirectURI string,
 	hashes []string,
+	validateFunc OIDCClientValidatorFunc,
 ) (*configv1alpha1.OIDCClient, *corev1.Secret) {
-	return fullyCapableOIDCClient(namespace, clientID, clientUID, redirectURI),
-		OIDCClientSecretStorageSecretForUID(t, namespace, clientUID, hashes)
+	allScopes := allDynamicClientScopes()
+
+	allGrantTypes := []configv1alpha1.GrantType{
+		"authorization_code", "urn:ietf:params:oauth:grant-type:token-exchange", "refresh_token",
+	}
+
+	return OIDCClientAndStorageSecret(t, namespace, clientID, clientUID, allGrantTypes, allScopes, redirectURI, hashes, validateFunc)
+}
+
+// OIDCClientAndStorageSecret returns an OIDC client which is allowed to use the specified grant types and scopes,
+// along with a corresponding client secret storage Secret. It also validates the client to make sure that the specified
+// combination of grant types and scopes is considered valid before returning the client.
+func OIDCClientAndStorageSecret(
+	t *testing.T,
+	namespace string,
+	clientID string,
+	clientUID string,
+	allowedGrantTypes []configv1alpha1.GrantType,
+	allowedScopes []configv1alpha1.Scope,
+	redirectURI string,
+	hashes []string,
+	validateFunc OIDCClientValidatorFunc,
+) (*configv1alpha1.OIDCClient, *corev1.Secret) {
+	oidcClient := newOIDCClient(namespace, clientID, clientUID, redirectURI, allowedGrantTypes, allowedScopes)
+	secret := OIDCClientSecretStorageSecretForUID(t, namespace, clientUID, hashes)
+
+	// If a test made an invalid OIDCClient then inform the author of the test, so they can fix the test case.
+	// This is an easy mistake to make when writing tests because there are lots of validations on OIDCClients.
+	valid, conditions, _ := validateFunc(oidcClient, secret, bcrypt.MinCost)
+	require.True(t, valid, "Test's OIDCClient should have been valid. See conditions for errors: %s", conditions)
+
+	return oidcClient, secret
 }

internal/testutil/oidctestutil/oidctestutil.go

@@ -1064,14 +1064,22 @@ func validateAuthcodeStorage(
 
 	// Check the user's identity, which are put into the downstream ID token's subject, username and groups claims.
 	require.Equal(t, wantDownstreamIDTokenSubject, actualClaims.Subject)
-	require.Equal(t, wantDownstreamIDTokenUsername, actualClaims.Extra["username"])
+	wantDownstreamIDTokenUsernameClaimToExist := 1
+	if wantDownstreamIDTokenUsername == "" {
+		wantDownstreamIDTokenUsernameClaimToExist = 0
+		require.NotContains(t, actualClaims.Extra, "username")
+	} else {
+		require.Equal(t, wantDownstreamIDTokenUsername, actualClaims.Extra["username"])
+	}
 	if slices.Contains(wantDownstreamGrantedScopes, "groups") {
-		require.Len(t, actualClaims.Extra, 2)
+		require.Len(t, actualClaims.Extra, wantDownstreamIDTokenUsernameClaimToExist+1)
 		actualDownstreamIDTokenGroups := actualClaims.Extra["groups"]
 		require.NotNil(t, actualDownstreamIDTokenGroups)
 		require.ElementsMatch(t, wantDownstreamIDTokenGroups, actualDownstreamIDTokenGroups)
 	} else {
-		require.Len(t, actualClaims.Extra, 1)
+		require.Emptyf(t, wantDownstreamIDTokenGroups, "test case did not want the groups scope to be granted, "+
+			"but wanted something in the groups claim, which doesn't make sense. please review the test case's expectations.")
+		require.Len(t, actualClaims.Extra, wantDownstreamIDTokenUsernameClaimToExist)
 		actualDownstreamIDTokenGroups := actualClaims.Extra["groups"]
 		require.Nil(t, actualDownstreamIDTokenGroups)
 	}

internal/testutil/psession.go

@@ -24,6 +24,7 @@ func NewFakePinnipedSession() *psession.PinnipedSession {
 			Subject:   "panda",
 		},
 		Custom: &psession.CustomSessionData{
+			Username:     "fake-username",
 			ProviderUID:  "fake-provider-uid",
 			ProviderType: "fake-provider-type",
 			ProviderName: "fake-provider-name",