OAuth specification 2.0 is out there since 2012 but 1.0a version is still widely used. Atlassian’s Jira is for example such case. You wouldn’t find anything about 1-Legged OAuth in the documentation but the fact is, by now, Jira is still supporting this flow but referring to this wrongly as 2-Legged OAuth. Sadly there aren’t lot of .Net Core libraries which implements OAuth’s 1-Legged, as described in the The OAuth Bible. I implemented this functionality into oauth-dotnetcore library and will show you how this can be used to access Jira APIs.