fix: Refactored Go SDK to use Go oauth2 client, added x-looker-appid header to Go requests

[jeremytchang]

Fixes #1027

• Refactored to use Go's standard oauth2 client to handle our client credentials flow. The client will automatically fetch and refresh the token when it is expired. Removed all the manual authorization implementation.

• Also updated the the AuthSession to maintain only one client instead of creating a new one per request. As recommended by Go docs. Clients and Transports are safe for concurrent use by multiple goroutines and for efficiency should only be created once and re-used. client docs

• Added x-looker-appid header with standard go http middleware, the RoundTripper interface. Article because the docs are sparse on this one.

• Removed auth implementation specific tests. Added couple auth sanity tests even though the go client itself is well tested. Updated tests to properly call NewAuthSession to properly create the client.

[github-actions]

Go Tests

  6 files  ±0    6 suites  ±0   4m 10s ⏱️ -41s
39 tests  - 3  39 ✔️  - 3  0 💤 ±0  0 ❌ ±0 
96 runs   - 6  96 ✔️  - 6  0 💤 ±0  0 ❌ ±0 

Results for commit 2ed10f0. ± Comparison against base commit 350d32d.

This pull request removes 13 and adds 10 tests. Note that renamed tests count towards both.

rtl ‑ TestAuthSession_Authenticate
rtl ‑ TestAuthSession_Authenticate/Authenticate()_errors_if_/login_errors_when_fetching_new_Access_Token_if_old_AccessToken_is_expired
rtl ‑ TestAuthSession_Authenticate/Authenticate()_fetches_new_Access_Token_from_/login_and_sets_header_with_it_if_old_AccessToken_is_expired
rtl ‑ TestAuthSession_Authenticate/Authenticate()_sets_header_with_current_AccessToken_if_not_expired
rtl ‑ TestAuthSession_Do
rtl ‑ TestAuthSession_Do/Do()_json_decodes_response_as_map[string]interface{}_type_if_result_is_interface{}_type
rtl ‑ TestAuthSession_Do/Do()_json_decodes_response_as_struct_type_if_result_is_struct_type
rtl ‑ TestAuthSession_Do/Do()_parses_response_as_string_type_if_result_is_string_type
rtl ‑ TestAuthSession_Do/Do()_unmarshals_num_type_field_to_string_type_field
rtl ‑ TestAuthSession_Do/Do()_unmarshals_string_type_field_to_num_type_field
…

rtl ‑ TestAuthSession_Do_Authorization
rtl ‑ TestAuthSession_Do_Authorization/Do()_sets_Authorization_header_with_access_token_fetched_from_/login
rtl ‑ TestAuthSession_Do_Authorization/Do()_sets_Authorization_header_with_new_access_token_fetched_from_/login_if_previous_access_token_expired
rtl ‑ TestAuthSession_Do_Parse
rtl ‑ TestAuthSession_Do_Parse/Do()_json_decodes_response_as_map[string]interface{}_type_if_result_is_interface{}_type
rtl ‑ TestAuthSession_Do_Parse/Do()_json_decodes_response_as_struct_type_if_result_is_struct_type
rtl ‑ TestAuthSession_Do_Parse/Do()_parses_response_as_string_type_if_result_is_string_type
rtl ‑ TestAuthSession_Do_Parse/Do()_unmarshals_num_type_field_to_string_type_field
rtl ‑ TestAuthSession_Do_Parse/Do()_unmarshals_string_type_field_to_num_type_field
rtl ‑ TestAuthSession_Do_Parse/Do{}_unmarshals_struct_with_mixed_string_and_num_types_correctly

[github-actions]

Go Tests

  6 files    6 suites   4m 42s ⏱️
39 tests 39 ✔️ 0 💤 0 ❌
96 runs  96 ✔️ 0 💤 0 ❌

Results for commit 38e0d5c.

[jkaster]

LGTM. Nice cleanup.

[github-actions]

Go Tests

  6 files    6 suites   5m 0s ⏱️
39 tests 39 ✔️ 0 💤 0 ❌
96 runs  96 ✔️ 0 💤 0 ❌

Results for commit 7a4dd9e.