Citing sources verbally in a speech works similarly to how journalists cite sources in magazine and newspaper article. In both cases, you need to provide both the citation and the context to help your audience understand the authority of the source.
Be brief, but provide enough information that your audience can track down the source. Highlight what is most important criteria for that source. Include who,what, when, and why the source is credible.
Use a combination of two or more of the following to verbally cite a source and relay credibility to your audience:
Handouts from Sprague Library, links to Excelsior University's Online Writing Lab, and more.