Interface naming convention Golang

In your case I would just name them RoleChecker and RoleAssumer, the “merged” one RoleCheckerAssumer. Or if you’d go with a single interface, that could be RoleHelper or RoleChecker.

ServerSession is also fine, or even just Session (especially if there is no “client” session). ServerSessioner on the other hand is bad, Session is not a verb and not a method of the interface.

There has been many posts about the conventions.

Effective Go: Interface names:

By convention, one-method interfaces are named by the method name plus an -er suffix or similar modification to construct an agent noun: Reader, Writer, Formatter, CloseNotifier etc.

There are a number of such names and it’s productive to honor them and the function names they capture. Read, Write, Close, Flush, String and so on have canonical signatures and meanings. To avoid confusion, don’t give your method one of those names unless it has the same signature and meaning. Conversely, if your type implements a method with the same meaning as a method on a well-known type, give it the same name and signature; call your string-converter method String not ToString.

Interface Types @ What’s in a name? – Talks at golang.org

Interfaces that specify just one method are usually just that function name with ‘er’ appended to it.

type Reader interface {
    Read(p []byte) (n int, err error)
}

Sometimes the result isn’t correct English, but we do it anyway:

type Execer interface {
    Exec(query string, args []Value) (Result, error)
}

Sometimes we use English to make it nicer:

type ByteReader interface {
    ReadByte() (c byte, err error)
}

When an interface includes multiple methods, choose a name that accurately describes its purpose (examples: net.Conn, http.ResponseWriter, io.ReadWriter).

For receiver names, don’t use this or self or similar ones. Instead:

Receivers @ What’s in a name? – Talks at golang.org

Receivers are a special kind of argument.

By convention, they are one or two characters that reflect the receiver type,
because they typically appear on almost every line:

func (b *Buffer) Read(p []byte) (n int, err error)

func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request)

func (r Rectangle) Size() Point

Receiver names should be consistent across a type’s methods.
(Don’t use r in one method and rdr in another.)

Go Code Review Comments: Receiver Names:

The name of a method’s receiver should be a reflection of its identity; often a one or two letter abbreviation of its type suffices (such as “c” or “cl” for “Client”). Don’t use generic names such as “me”, “this” or “self”, identifiers typical of object-oriented languages that place more emphasis on methods as opposed to functions. The name need not be as descriptive as that of a method argument, as its role is obvious and serves no documentary purpose. It can be very short as it will appear on almost every line of every method of the type; familiarity admits brevity. Be consistent, too: if you call the receiver “c” in one method, don’t call it “cl” in another.