Swagger UI passing authentication token to API call in header

@ApiImplicitParams and @ApiImplicitParam should do the trick:

@GET
@Produces("application/json")
@ApiImplicitParams({
    @ApiImplicitParam(name = "Authorization", value = "Authorization token", 
                      required = true, dataType = "string", paramType = "header") })
public String getUser(@PathParam("username") String userName) {
    ...
}

From the documentation:

You may wish you describe operation parameters manually. This can be for various reasons, for example:

• Using Servlets which don’t use JAX-RS annotations.
• Wanting to hide a parameter as it is defined and override it with a completely different definition.
• Describe a parameter that is used by a filter or another resource prior to reaching the JAX-RS implementation.

The Swagger UI will be updated so you can send your token from there. No changes to HTML will be necessary.

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_{Note: A while ago, when documenting a REST API with Swagger, I realized that just adding @ApiImplicitParam is not enough (even if you have only one parameter). Anyway, you must add @ApiImplicitParams too.}