mito: allow use of Basic Authentication and OAuth2 in command

[efd6]

This allows use of the configuration options available in the Filebeat input to improve parity for development playground purposes. The implementation is simpler here and does not make use of the go-ucfg package, so there are some differences in config behaviour. Only limited validation of the config is performed.

Configuration is in the YAML exposed via the cfg option. The options available are similarly interpreted as the config in Filebeat with the options corresponding to the following structs:

type config struct {
	Globals map[string]interface{} `yaml:"globals"`
	Regexps map[string]string      `yaml:"regexp"`
	Auth    *authConfig            `yaml:"auth"`
}

type authConfig struct {
	Basic  *lib.BasicAuth `yaml:"basic"`
	OAuth2 *oAuth2        `yaml:"oauth2"`
}

type oAuth2 struct {
	Provider string `yaml:"provider"`

	ClientID       string     `yaml:"client.id"`
	ClientSecret   *string    `yaml:"client.secret"`
	EndpointParams url.Values `yaml:"endpoint_params"`
	Password       string     `yaml:"password"`
	Scopes         []string   `yaml:"scopes"`
	TokenURL       string     `yaml:"token_url"`
	User           string     `yaml:"user"`

	GoogleCredentialsFile  string `yaml:"google.credentials_file"`
	GoogleCredentialsJSON  string `yaml:"google.credentials_json"`
	GoogleJWTFile          string `yaml:"google.jwt_file"`
	GoogleJWTJSON          string `yaml:"google.jwt_json"`
	GoogleDelegatedAccount string `yaml:"google.delegated_account"`

	AzureTenantID string `yaml:"azure.tenant_id"`
	AzureResource string `yaml:"azure.resource"`
}

Please take a look.

[andrewkroh]

Consider adding a test case to check that basic auth is being passed though in requests.

[efd6]

That was a little tricky, but done. The OAuth2 case could also be tested, but will require significant additional complexity to be added to the test supports.