oauth2/openid authorization flows use different User-Agent

[ptman]

@oauth2_tokenEndpoint = /token
@oauth2_clientId = foo
@oauth2_clientSecret = bar
GET /baz
Authorization: oauth2 client_credentials

The /token request is made with User-Agent: got (https://github.com/sindresorhus/got) while the /baz request is made with User-Agent: httpyac. Consistency would be great.

[ptman]

Missing call to setDefaultHttpyacHeaders() or setting headers around

httpyac/src/plugins/oauth2/flow/clientCredentialsFlow.ts

Line 28 in 4e3b601

body: utils.toQueryParams({