Hey, so somebody asked this question about blowjobs a little while ago, which actually turned into an interesting opportunity to talk about penance. It's important to separate - which pop culture often doesn't - secular punishment and religious penance. It could very much be the case that an offence have both a legal punishment and a religious penance. It's important to remember that the act of penance should, at its heart, be voluntary. These were acts undertaken to safeguard the very soul from eternal damnation, after all.

At least for the Early Medieval period, the Church is a big fan of fasting and prayer, in particular the singing of psalms, as penance. We have a number of medieval penitentials (books of prescribed penances for a variety of offences), such as the early 11th Century Scriftboc, an anonymous penitential and handbook surviving in Cotton manuscripts Junius and Tiberius respectively, and the Paenitentiale Theodori or Canons of Theodore written by Saint Theodore of Tarsus, Archbishop of Canterbury from 668 to 690.

Theodore, for example, recommends:

If anyone scorns a commanded fast among God's people and against the decree of the witan or the confessor, he is to fast 40 days, not counting the ordained fasts and the Lenten fast. If he does it often and it is customary for him, he is to be driven from God's church as the Lord himself said: "If any man seduces one of these , it would be better for him that a millstone were tied around his neck and he were thrown into the sea."

The MS Tiberius handbook, among its penitentials, states:

If someone with fraud takes a woman or a maiden forcibly in unlawful fornication against her will, he is to be excommunicated.

This is a severe punishment, and it is one of those cases where there are both legal and moral consequences. Alfred's Doomboc lists a variety of scales of wergild for a gradual scale of sexual assault, which would be liable to civil authorities, alongside the spiritual.