oidcccl: v23.2.3: nil pointer in authentication_oidc

This issue was auto filed by Sentry. It represents a crash or reported error on a live cluster with telemetry enabled.

Sentry Link: [https://cockroach-labs.sentry.io/issues/5936651958/?referrer=webhooks_plugin](https://cockroach-labs.sentry.io/issues/5936651958/?referrer=webhooks_plugin)

Panic Message:

```
panic.go:914: runtime error: invalid memory address or nil pointer dereference
(1) attached stack trace
-- stack trace:
| runtime.gopanic
| GOROOT/src/runtime/panic.go:914
| runtime.panicmem
| GOROOT/src/runtime/panic.go:261
| runtime.sigpanic
| GOROOT/src/runtime/signal_unix.go:861
| github.com/cockroachdb/cockroach/pkg/ccl/oidcccl.glob..func2.3
| github.com/cockroachdb/cockroach/pkg/ccl/oidcccl/authentication_oidc.go:728
| net/http.HandlerFunc.ServeHTTP
| GOROOT/src/net/http/server.go:2136
| net/http.(*ServeMux).ServeHTTP
| GOROOT/src/net/http/server.go:2514
| net/http.HandlerFunc.ServeHTTP
| GOROOT/src/net/http/server.go:2136
| github.com/NYTimes/gziphandler.NewGzipLevelAndMinSize.func1.1
| github.com/NYTimes/gziphandler/external/com_github_nytimes_gziphandler/gzip.go:253
| net/http.HandlerFunc.ServeHTTP
| GOROOT/src/net/http/server.go:2136
| github.com/cockroachdb/cockroach/pkg/server.(*nodeProxy).nodeProxyHandler
| github.com/cockroachdb/cockroach/pkg/server/node_http_router.go:63
| github.com/cockroachdb/cockroach/pkg/server.(*httpServer).baseHandler
| github.com/cockroachdb/cockroach/pkg/server/server_http.go:381
| github.com/cockroachdb/cockroach/pkg/server.(*serverController).httpMux
| github.com/cockroachdb/cockroach/pkg/server/server_controller_http.go:132
| net/http.HandlerFunc.ServeHTTP
| GOROOT/src/net/http/server.go:2136
| net/http.serverHandler.ServeHTTP
| GOROOT/src/net/http/server.go:2938
| net/http.(*conn).serve
| GOROOT/src/net/http/server.go:2009
| runtime.goexit
| src/runtime/asm_amd64.s:1650
Wraps: (2) runtime error: invalid memory address or nil pointer dereference
Error types: (1) *withstack.withStack (2) runtime.errorString
-- report composition:
runtime.errorString
panic.go:914: *withstack.withStack (top exception)
```

Stacktrace (expand for inline code snippets):

[src/runtime/asm_amd64.s#L1649-L1651](src/runtime/asm_amd64.s#L1649-L1651)
[GOROOT/src/net/http/server.go#L2008-L2010](GOROOT/src/net/http/server.go#L2008-L2010)
[GOROOT/src/net/http/server.go#L2937-L2939](GOROOT/src/net/http/server.go#L2937-L2939)
[GOROOT/src/net/http/server.go#L2135-L2137](GOROOT/src/net/http/server.go#L2135-L2137)
[https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/server_controller_http.go#L131-L133](https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/server_controller_http.go#L131-L133)
[https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/server_http.go#L380-L382](https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/server_http.go#L380-L382)
[https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/node_http_router.go#L62-L64](https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/server/node_http_router.go#L62-L64)
[GOROOT/src/net/http/server.go#L2135-L2137](GOROOT/src/net/http/server.go#L2135-L2137)
[github.com/NYTimes/gziphandler/external/com_github_nytimes_gziphandler/gzip.go#L252-L254](github.com/NYTimes/gziphandler/external/com_github_nytimes_gziphandler/gzip.go#L252-L254)
[GOROOT/src/net/http/server.go#L2135-L2137](GOROOT/src/net/http/server.go#L2135-L2137)
[GOROOT/src/net/http/server.go#L2513-L2515](GOROOT/src/net/http/server.go#L2513-L2515)
[GOROOT/src/net/http/server.go#L2135-L2137](GOROOT/src/net/http/server.go#L2135-L2137)
[https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/ccl/oidcccl/authentication_oidc.go#L727-L729](https://github.com/cockroachdb/cockroach/blob/03498e5964c0eaa45bb5435b4c600de38d542910/pkg/ccl/oidcccl/authentication_oidc.go#L727-L729)
[GOROOT/src/runtime/signal_unix.go#L860-L862](GOROOT/src/runtime/signal_unix.go#L860-L862)
[GOROOT/src/runtime/panic.go#L260-L262](GOROOT/src/runtime/panic.go#L260-L262)
[GOROOT/src/runtime/panic.go#L913-L915](GOROOT/src/runtime/panic.go#L913-L915)

```
src/runtime/asm_amd64.s in runtime.goexit at line 1650
GOROOT/src/net/http/server.go in net/http.(*conn).serve at line 2009
GOROOT/src/net/http/server.go in net/http.serverHandler.ServeHTTP at line 2938
GOROOT/src/net/http/server.go in net/http.HandlerFunc.ServeHTTP at line 2136
pkg/server/server_controller_http.go in pkg/server.(*serverController).httpMux at line 132
pkg/server/server_http.go in pkg/server.(*httpServer).baseHandler at line 381
pkg/server/node_http_router.go in pkg/server.(*nodeProxy).nodeProxyHandler at line 63
GOROOT/src/net/http/server.go in net/http.HandlerFunc.ServeHTTP at line 2136
github.com/NYTimes/gziphandler/external/com_github_nytimes_gziphandler/gzip.go in github.com/NYTimes/gziphandler.NewGzipLevelAndMinSize.func1.1 at line 253
GOROOT/src/net/http/server.go in net/http.HandlerFunc.ServeHTTP at line 2136
GOROOT/src/net/http/server.go in net/http.(*ServeMux).ServeHTTP at line 2514
GOROOT/src/net/http/server.go in net/http.HandlerFunc.ServeHTTP at line 2136
pkg/ccl/oidcccl/authentication_oidc.go in pkg/ccl/oidcccl.glob..func2.3 at line 728
GOROOT/src/runtime/signal_unix.go in runtime.sigpanic at line 861
GOROOT/src/runtime/panic.go in runtime.panicmem at line 261
GOROOT/src/runtime/panic.go in runtime.gopanic at line 914
```

### Tags

| Tag | Value |
| --- | --- |
| Command | server |
| Environment | v23.2.3 |
| Go Version | go1.21.5 X:nocoverageredesign |
| Platform | linux amd64 |
| Distribution | CCL |
| Cockroach Release | v23.2.3 |
| Cockroach SHA | 03498e5964c0eaa45bb5435b4c600de38d542910 |
| # of CPUs | 2 |
| # of Goroutines | 388 |

Jira issue: CRDB-42652

Epic CRDB-54682