fix(oauth): prevent panic when using JWK auth

[milas]

Summary

When building the client assertion for JWK auth mode, "" is being passed for the client ID and nil is being passed for the signer.

SDK config:

okta.WithAuthorizationMode("JWK")
okta.WithJWK(jwkValue)
okta.WithEncryptionType("RSA")

Panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x103232ab8]

goroutine 1 [running]:
github.com/go-jose/go-jose/v3/jwt.(*signedBuilder).sign(0x1400016cd08)
	/Users/milas/dev/go/pkg/mod/github.com/go-jose/go-jose/[email protected]/jwt/builder.go:225 +0x58
github.com/go-jose/go-jose/v3/jwt.(*signedBuilder).CompactSerialize(0x0?)
	/Users/milas/dev/go/pkg/mod/github.com/go-jose/go-jose/[email protected]/jwt/builder.go:198 +0x1c
github.com/okta/okta-sdk-golang/v5/okta.createClientAssertion({0x103424595, 0x1e}, {0x0, 0x0}, {0x0, 0x0})
	/Users/milas/dev/go/pkg/mod/github.com/okta/okta-sdk-golang/[email protected]/okta/client.go:691 +0x18c
github.com/okta/okta-sdk-golang/v5/okta.getAccessTokenForPrivateKey(0x14000142390, {0x103424595, 0x1e}, {0x1400016e2c0, 0x2b4}, {0x140000c0580, 0x32}, {0x1400009ec80, 0x1, 0x1}, ...)
	/Users/milas/dev/go/pkg/mod/github.com/okta/okta-sdk-golang/[email protected]/okta/client.go:731 +0x930
github.com/okta/okta-sdk-golang/v5/okta.(*JWKAuth).Authorize(0x140000e4180, {0x103415198, 0x3}, {0x140000c05c0, 0x2a})
	/Users/milas/dev/go/pkg/mod/github.com/okta/okta-sdk-golang/[email protected]/okta/client.go:582 +0x538
github.com/okta/okta-sdk-golang/v5/okta.(*APIClient).prepareRequest(0x1400011c688, {0x10370f270, 0x103a92800}, {0x140000d0b10, 0x26}, {0x103415198, 0x3}, {0x0?, 0x0?}, 0x14000039c18, ...)
	/Users/milas/dev/go/pkg/mod/github.com/okta/okta-sdk-golang/[email protected]/okta/client.go:1256 +0x14d0

Fixes N/A

Type of PR

• Bug Fix (non-breaking fixes to existing functionality)
• New Feature (non-breaking changes that add new functionality)
• Documentation update
• Test Updates
• Other (Please describe the type)

Test Information

• My PR required test updates

Go Version: 1.25.0
Os Version: n/a
OpenAPI Spec Version: n/a

Signoff

• I have submitted a CLA for this PR
• Each commit message explains what the commit does
• I have updated documentation to explain what my PR does
• My code is covered by tests if required
• I ran make fmt on my code
  • I did this but it changed a TON of unrelated stuff; my commit is properly formatted though
• I did not edit any automatically generated files

[milas]

FYI I believe the JWTAuth might be broken as well, but I am not using that so was not confident in making a fix there.

[github-actions]

This PR has been marked stale because there has been no activity within the last 28 days. To keep this PR active, remove the stale label.