panic: runtime error when saml app has no embed_url

[jon-parodi-yohana]

When using the preconfigured saml app that has no associated embedded urls, provider crashes during future plans.
This is explicitly reproducible with the preconfigured app 'radius_generic_wifi' and was introduced in version 3.32
In versions 3.28-3.31 this error does not present itself.

Steps to reproduce:

resource "okta_app_saml" "radius_app" {
    accessibility_self_service = false
    app_settings_json          = jsonencode({})
    auto_submit_toolbar        = false
    hide_ios                   = false
    hide_web                   = false
    honor_force_authn          = false
    label                      = "hillview-wifi"
    preconfigured_app          = "radius_generic_app"
    saml_version               = "2.0"
    skip_groups                = false
    skip_users                 = false
    status                     = "ACTIVE"
}
resource "okta_group" "radius_role" {
       description = "hillview-wifi user role"
       name        = "app-hillview-wifi-user"
       skip_users  = false
}
resource "okta_app_group_assignment" "radius_group_assignment" {
       priority          = 1
       retain_assignment = false
       group_id = okta_group.radius_role.id
       app_id = okta_app_saml.radius_app.id
}

Stack trace:

panic: runtime error: index out of range [0] with length 0

goroutine 88 [running]:
github.com/okta/terraform-provider-okta/okta.linksValue({0x18c9800, 0xc00000db00}, {0xc000625200, 0x8, 0xffffffffffffff01})
        github.com/okta/terraform-provider-okta/okta/links.go:9 +0x175
github.com/okta/terraform-provider-okta/okta.linksValue({0x1917360, 0xc00083a870}, {0xc0006251f0, 0x2, 0x2})
        github.com/okta/terraform-provider-okta/okta/links.go:25 +0x145
github.com/okta/terraform-provider-okta/okta.resourceAppSamlRead({0x1b7a768, 0xc00080c7e0}, 0xc000399900, {0x1905920, 0xc0002c1680})
        github.com/okta/terraform-provider-okta/okta/resource_okta_app_saml.go:491 +0x5b8
github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema.(*Resource).read(0xc000319b20, {0x1b7a7a0, 0xc00060e540}, 0xd, {0x1905920, 0xc0002c1680})
        github.com/hashicorp/terraform-plugin-sdk/v2@v2.19.0/helper/schema/resource.go:724 +0x12e
github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema.(*Resource).RefreshWithoutUpgrade(0xc000319b20, {0x1b7a7a0, 0xc00060e540}, 0xc000691110, {0x1905920, 0xc0002c1680})
        github.com/hashicorp/terraform-plugin-sdk/v2@v2.19.0/helper/schema/resource.go:1015 +0x585
github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema.(*GRPCProviderServer).ReadResource(0xc0001282a0, {0x1b7a7a0, 0xc0003404b0}, 0xc0001b3180)
        github.com/hashicorp/terraform-plugin-sdk/v2@v2.19.0/helper/schema/grpc_provider.go:613 +0x574
github.com/hashicorp/terraform-plugin-go/tfprotov5/tf5server.(*server).ReadResource(0xc0001a4320, {0x1b7a7a0, 0xc00025b830}, 0xc000306540)
        github.com/hashicorp/terraform-plugin-go@v0.12.0/tfprotov5/tf5server/server.go:747 +0x472
github.com/hashicorp/terraform-plugin-go/tfprotov5/internal/tfplugin5._Provider_ReadResource_Handler({0x19e47e0, 0xc0001a4320}, {0x1b7a7a0, 0xc00025b830}, 0xc000262070, 0x0)
        github.com/hashicorp/terraform-plugin-go@v0.12.0/tfprotov5/internal/tfplugin5/tfplugin5_grpc.pb.go:349 +0x170
google.golang.org/grpc.(*Server).processUnaryRPC(0xc000326a80, {0x1b8ad60, 0xc00056e9c0}, 0xc000650360, 0xc00011f740, 0x215a050, 0x0)
        google.golang.org/grpc@v1.48.0/server.go:1295 +0xb03
google.golang.org/grpc.(*Server).handleStream(0xc000326a80, {0x1b8ad60, 0xc00056e9c0}, 0xc000650360, 0x0)
        google.golang.org/grpc@v1.48.0/server.go:1636 +0xa2a
google.golang.org/grpc.(*Server).serveStreams.func1.2()
        google.golang.org/grpc@v1.48.0/server.go:932 +0x98
created by google.golang.org/grpc.(*Server).serveStreams.func1
        google.golang.org/grpc@v1.48.0/server.go:930 +0x294

Error: The terraform-provider-okta_v3.32.0 plugin crashed!

This is always indicative of a bug within the plugin. It would be immensely
helpful if you could report the crash with the plugin's maintainers so that it
can be fixed. The output above should help diagnose the issue.

Failure appears to occur at

terraform-provider-okta/okta/resource_okta_app_saml.go

Line 491 in fb7c249

_ = d.Set("embed_url", linksValue(app.Links, "appLinks", "href"))

and crashes due to there being no links being provided and no logic to validate

[monde]

Thanks @jon-parodi-yohana . I hate panics and this will be an easy fix.
Okta internal reference: https://oktainc.atlassian.net/browse/OKTA-585994