OIDC config to allow mismatched discovery / issuer

 - There are a number of cases where the OIDC discovery url returns one
   issuer, but its desirable to use a separately configured / named
   issuer for validation instead.

   There are cases in Azure where this is necessary due to their
   non-standard OIDC configuration -- which is why this was originally
   added:
   coreos/go-oidc#315

   There are also cases where it's necessary to use an in-cluster
   service address, but browser clients are using the external ingress
   address. Due to cluster DNS configuration, it's possible that
   flyteadmin may be unable to resolve or use the public ingress
   address for an Idp, but the internal service address is available.
   This configuration change allows for that.

flyteadmin/auth/auth_context.go

@@ -141,6 +141,12 @@ func NewAuthenticationContext(ctx context.Context, sm core.SecretManager, oauth2
 	// Construct an oidc Provider, which needs its own http Client.
 	oidcCtx := oidc.ClientContext(ctx, httpClient)
 	baseURL := options.UserAuth.OpenID.BaseURL.String()
+	// use a different issuer for token validation if configured
+	// this allows discovery to work when issuer_url from upstream is mismatched
+	// see https://github.com/coreos/go-oidc/pull/315
+	if iss := options.UserAuth.OpenID.IssuerURL.String(); iss != "" {
+		oidcCtx = oidc.InsecureIssuerURLContext(oidcCtx, iss)
+	}
 	provider, err := oidc.NewProvider(oidcCtx, baseURL)
 	if err != nil {
 		return Context{}, errors.Wrapf(ErrauthCtx, err, "Error creating oidc provider w/ issuer [%v]", baseURL)

flyteadmin/auth/config/config.go

@@ -267,6 +267,12 @@ type OpenIDOptions struct {
 	// will look something like https://company.okta.com/oauth2/abcdef123456789/
 	BaseURL config.URL `json:"baseUrl"`
 
+	// Allows discovery to work when the issuer_url reported by upstream is mismatched with baseUrl. This may be the
+	// case with Azure *or* when baseUrl refers to an in-cluster service like https://keycloak/auth/realms/MyRealm but
+	// the issuer is a public ingress address accessible to the OIDC client
+	// Refer to https://github.com/coreos/go-oidc/pull/315 for additional details
+	IssuerURL config.URL `json:"issuerUrl" pflag:",OPTIONAL: Use this issuer URL for request validation rather than baseUrl."`
+
 	// Provides a list of scopes to request from the IDP when authenticating. Default value requests claims that should
 	// be supported by any OIdC server. Refer to https://openid.net/specs/openid-connect-core-1_0.html#ScopeClaims for
 	// a complete list. Other providers might support additional scopes that you can define in a config.

flyteadmin/auth/config/config_test.go

@@ -50,6 +50,9 @@ func TestParseClientSecretConfig(t *testing.T) {
 func TestDefaultConfig(t *testing.T) {
 	assert.Equal(t, len(DefaultConfig.AppAuth.SelfAuthServer.StaticClients), 3)
 	assert.Equal(t, DefaultConfig.AppAuth.SelfAuthServer.StaticClients["flyte-cli"].ID, "flyte-cli")
+
+	// oidc issuer config should only be used when baseUrl is mismatched
+	assert.Equal(t, DefaultConfig.UserAuth.OpenID.IssuerURL.String(), "")
 }
 
 func TestCompare(t *testing.T) {